Microbiol Mol Biol Rev, June 1998, p. 249-274, Vol. 62, No. 2
Department of Biochemistry and Biophysics,
School of Medicine, University of California, San Francisco,
California 94143-0448
1092-2172/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Signalling in the Yeasts: An Informational
Cascade with Links to the Filamentous Fungi
SUMMARY
INTRODUCTION
MAPK CASCADE MODULE AND SIGNAL TRANSDUCTION
THE YING AND YANG OF RESPONSE TO OSMOLARITY: HOG, STY, AND
PKC PATHWAYS
Response to High Osmolarity in S. cerevisiae and
S. pombe
Activation of the Hog1 MAPK cascade by two different
sensors.
Osmosensing involves a multistep phosphorelay system related
to the histidyl-aspartyl phosphorelay systems of bacteria.
Mutations that turn the pathway on or off
use of epistasis
relationships to order pathway components.
Stress response element.
Response to Stress via the Sty1 MAPK Pathway in
S. pombeCoordination of Multiple Distinct
Outputs in Response to Stress
The components of the Sty1 MAPK pathway are homologous to
those of the HOG pathway of S. cerevisiae.
A transcription factor with similarity to mammalian ATF2 is
the target of the MAPK cascade.
Links between the Sty pathway and cell size control at
mitosis.
Identification and order of some of the pathway components.
Integration of the response to stress with sexual
development.
PKC Pathway in S. cerevisiae and
Response to Low Osmolarity
PKC MAPK cascade and its activation.
(i) Activation by Pkc1.
(ii) Activation by pheromones.
Rho1 regulates Pkc1 and glucan synthase.
(i)
Activation of Pkc1.
(ii) Rho1 activates glucan synthase.
Targets of the PKC pathway.
(i) Rlm1, a transcriptional factor downstream of Mpk1.
(ii) Genes for cell wall biosynthesis.
Hcs77, a putative receptor that senses membrane
stretch.
PHEROMONE RESPONSE MAPK CASCADE FOR MATING, MEIOSIS, AND
FILAMENTOUS GROWTH
Pheromone Response Pathway in S. cerevisiae
MAPK cascade and Ste5 scaffold.
Upstream of the MAPK cascade: pheromones, receptors, and
heterotrimeric G protein.
(i) Pheromones.
(ii) Receptors and heterotrimeric G proteins.
Ste20, a p65PAK protein involved in mating.
Identification of the components of the pathway.
Pheromone Response Pathway in S. pombe
MAPK cascade components.
Stepwise induction of mating and meiosis by nitrogen
starvation and pheromones.
Ras1 has a dual regulatory function: activation of the
pheromone MAPK cascade and activation of a polarity and cell morphology
cascade.
MAPK Cascade Signalling and Dimorphism
Pseudohyphal pathway of S. cerevisiae.
(i) MAPK cascade and transcriptional activators.
(ii) Upstream of the MAPK cascade.
(iii) Parallel pathways for pseudohyphal growth?
Signalling and dimorphism in other fungi: C. albicans and U. maydis.
Mate as You Wish: What Matters Is What You Are after
Mating
Events regulated by the A and B
complexes.
Multiple pheromones and receptors regulate a specialized
form of cell fusion.
Tales of G Proteins, Pheromones, and MAPK Components
Heterotrimeric G proteins.
MAPKK, MAPK, and pheromones.
CONCLUDING REMARKS
ACKNOWLEDGMENTS
REFERENCES
SUMMARY
 Top NextReferences
|
|---|
All cells, from bacteria and yeasts to mammalian cells, respond to cues from their environment. A variety of mechanisms exist for the transduction of these external signals to the interior of the cell, resulting in altered patterns of protein activity. Eukaryotic cells commonly transduce external cues via a conserved module composed of three protein kinases, the mitogen-activated protein kinase (MAPK) cascade. This module can then activate substrates, some of which include transcriptional activators. Multiple MAPK signalling pathways coexist in a cell. This review considers different MAPK cascade signalling pathways that govern several aspects of the life cycle of budding and fission yeasts: conjugation and meiosis by the pheromone response pathway, stress response by the high-osmolarity sensing pathway, cell wall biosynthesis in response to activation of the low-osmolarity and heat-sensing pathway, and pseudohyphal growth in response to activation of a subset of the components of the pheromone response pathway. Because the MAPK cascade components are highly conserved, a key question in studies of these pathways is the mechanism by which specificity of response is achieved. Several other issues to be addressed in this review concern the nature of the receptors used to sense the external signals and the mechanism by which the receptors communicate with other components leading to activation of the MAPK cascade. Recently, it has become apparent that MAPK cascades are important in governing the pathogenicity of filamentous fungi.
INTRODUCTION
|
TopPreviousNextReferences
|
|---|
The purpose of this review is to summarize the current knowledge
of signalling pathways in the yeasts for nonspecialists, particularly
for fungal biologists who are beginning studies in this area. This
review has been written to describe both how these pathways function
and how they were figured out
how the components in these different
pathways were identified, how they were ordered, and what kinds of
assays are used in such studies.
I describe several pathways in both Saccharomyces cerevisiae (budding yeast) and Schizosaccharomyces pombe (fission yeast), juxtaposing pathways used for the same response in an attempt to point out similarities and differences in the use of highly conserved components in different organisms. Several reasons have motivated me as a fungal biologist to do this. I am interested in cell-cell interactions between fungal cells and between fungal and plant cells. Because these interactions are likely to involve diverse signals and response pathways, an understanding of the different pathways that operate in the yeasts may be directly relevant to understanding the interactions of filamentous fungi with their environment and their hosts. The literature in the area of signalling is vast. I have therefore tried to extract some of the most important lessons to make this review accessible to nonspecialists, although I hope that specialists will also find it useful. Because information about signal transduction pathways in filamentous fungi is fragmentary, in many cases I have interspersed nuggets of information on this topic in the relevant sections describing the yeast pathways.
Several important general issues, which provide a framework for examining the different pathways, are as follows. (i) A given cell contains multiple pathways, each of which responds to a distinct signal that is transduced to give a specific response. Because the central component of these pathways, the mitogen-activated protein kinase (MAPK) cascade (see below), is highly conserved, the cell must have mechanisms for preventing inappropriate communication between pathways. One mechanism for preventing such cross talk involves scaffold or sequestering proteins. (ii) A given signalling component can be used in more than one pathway within the same cell to respond to different signals. This observation raises the question of how the specificity of the response is regulated in such cases. Specificity may involve modulation of the activity of a transcription factor by its association with different accessory proteins. (iii) Comparisons of pathways, for example, used for response to stress will illustrate that in one organism a pathway responds to only one stress signal whereas in another organism the same components are used to respond to a multitude of stress signals. We are then confronted with the question of how multiple input signals are integrated. One possibility is the use of a different sensor for each different signal. (iv) Different organisms use the same machinery to respond to the same signal, but some of the components of the machinery may be used differently. (v) The receptors used in different pathways are of different types: G-protein-coupled (serpentine or seven-transmembrane) receptors, His-Asp phosphorelay sensors, and a novel class of integral membrane proteins. In each case, a central issue (often unsolved) is how they communicate with downstream components. (vi) The responses elicited by the different signals are numerous and in many cases are common to all eukaryotes. In some cases, the response of a pathway to a given signal may serve to coordinate different processes, for example, osmolarity and mitosis or nutritional status and meiosis. (vii) A given pathway may link two different types of phosphorylation cascades. (viii) Many examples of redundancy of components are provided by the different pathways. (ix) Lastly, filamentous fungi may use some of the machinery used in the mating response in yeasts to regulate the intricacies of hyphal growth.
I first present a general introduction to the core of the signalling pathways, the MAPK cascade. I then describe the pathways that sense osmolarity in both yeasts and follow with a description of the pheromone response pathway. As part of the latter section, I discuss regulation of filamentous growth in the Basidiomycete fungi by pheromones and receptors. I also present information on the role of various signalling components in the life cycle of filamentous fungi. Each section has been written in a self-contained manner so that the reader can read the sections separately.
MAPK CASCADE MODULE AND SIGNAL TRANSDUCTION
|
TopPreviousNextReferences
|
|---|
All organisms, from bacteria and yeasts to mammalian cells, respond to cues from the extracellular environment. These cues are then transduced from the cell surface to the interior of the cell, resulting in patterns of altered gene expression and protein activity, which result in a cellular response to the external environment.
In eukaryotic cells, the MAPK cascade module is a key element in mediating the transduction of many signals generated at the cell surface to the nucleus (Fig. 1). Three protein kinases that are highly conserved in all eukaryotes make up this module: MAPK (also known as extracellular signal-regulated kinase [ERK]), MAPK kinase (MAPKK, also known as mitogen-activated, ERK-activating kinase [MEK]), and MAPK kinase kinase (MAPKKK, also known as MEK kinase [MEKK]). I will refer to them in this review as MAPK, MAPKK, and MAPKKK, respectively. Sequential activation of these kinases by phosphorylation lies at the heart of transduction of the signal through this kinase module. MAPK is activated by the dual-specificity serine/threonine tyrosine kinase MAPKK, and it is in turn activated by the serine/threonine kinase MAPKKK (reviewed in references 160, 175, and 183). The latter becomes activated in response to a signal generated by an input. Thus, input signals lead to activation of the MAPK cascade, which then generates output signals (Fig. 1).
|
The signal that leads to activation of the MAPK cascade is perceived by a variety of types of receptors: G-protein-coupled seven-transmembrane receptors, His-Asp phosphorelay sensors, receptor-tyrosine kinases, and integral membrane proteins (reviewed in reference 73). In the yeasts, serpentine receptors, His-Asp phosphorelay sensors, and integral membrane protein sensors have been identified. The budding yeast genome does not code for any receptor-tyrosine kinases (reviewed in reference 83). The target of activation of the MAPK cascade module is often a transcription factor (reviewed in references 76 and 208), although other targets have also been identified. Phosphorylation of a transcription factor by the MAPK can in principle increase its binding affinity, activation ability, or cellular location, resulting in increased transcription of target genes. Inactivation of the MAPK cascade by dual-specificity phosphatases and by tyrosine phosphatases is one mechanism for attenuation of the signal and adaptation to the response (reviewed in references 82 and 146).
In S. cerevisiae, independently acting MAPK cascades exist
that regulate response to osmotic stress, pheromones, perturbations of
cell wall integrity, spore formation, and pseudohyphal growth (reviewed
in reference 73). In S. pombe, fewer
pathwaysthose for response to osmotic stress and pheromoneshave
been characterized. I will discuss all of the above pathways except the
sporulation pathway.
The components of the MAPK cascade module are related to other kinases by virtue of their catalytic domain, which consists of approximately 250 to 300 amino acid residues. They catalyze the transfer of gamma phosphate from ATP to a hydroxyl residue on Ser and Thr or on Thr and Tyr (reviewed in reference 68).
The catalytic domain of all kinases can be subdivided into 12 conserved domains, within which 12 residues are invariant or highly conserved. These residues must thus be critical for activity of the kinase (reviewed in reference 68). Analyses of mutations of these highly conserved residues have been crucial in elucidation of the functional requirement of the kinase activity. The conserved primary structure of the catalytic domains suggests that they may fold into similar three-dimensional structures. The crystallographic structures of the catalytic domains of two mammalian MAPKs, ERK2 and p38, have demonstrated many similarities in their topology. Despite these similarities, differences were found in the ATP and substrate binding sites and in the phosphorylation lip (214, 232; see also reference 68). These variations in the topology may be important for the specificity of recognition by the activating MAPKK and for recognition of substrate.
MAPKs are activated by phosphorylation on two closely spaced Thr and Tyr residues (Thr-X-Tyr) found in catalytic subdomain VIII; X can be Pro, Gly, or Glu. Mutation of the X residue does not appear to affect activation by MAPKK (see reference 214 and references therein). The MAPKKs are activated by phosphorylation on two closely spaced serine residues or serine and threonine residues in domain VIII.
The MAPKKKs have a large N-terminal noncatalytic region and a C-terminal catalytic domain. The noncatalytic domain appears to be autoinhibitory, as inferred from the fact that deletion of this region causes constitutive activation of the kinase in the absence of a stimulus (see, for example, references 25 and 127). The mechanism by which MAPKKKs become activated remains to be elucidated and is the subject of current intensive studies. Conformational changes brought about by interaction with another protein or by self-dimerization or removal of a protein that inhibits the activation of the catalytic domain may be involved in such activation.
These introductory comments should help the reader put into perspective the MAPK cascade as we "tour the pathways."
THE YING AND YANG OF RESPONSE TO OSMOLARITY: HOG, STY, AND PKC PATHWAYS
|
TopPreviousNextReferences
|
|---|
S. cerevisiae cells detect and respond to high and low extracellular osmolarity by activating two different MAPK pathways, HOG and PKC. High osmolarity activates the HOG pathway, and low osmolarity activates the PKC pathway. I first describe the response to high osmolarity in budding yeast and compare it with that in fission yeast. I then describe the response to low osmolarity in budding yeast; little is known of such a response in fission yeast.
Studies of the HOG pathway have provided important insights into activation of MAPK pathways. One particularly notable feature of this pathway is that it exhibits multiple redundancies. First, there is redundancy at the sensor level. Two independently acting branches activate the MAPK cascade. In one branch, the osmosensor is a member of a His-Asp phosphorelay system. In the other, the osmosensor is a membrane protein with multiple membrane-spanning domains. Second, there is redundancy at the MAPKKK level: multiple MAPKKKs can activate the MAPKK. The branch linked to the His-Asp phosphorelay system utilizes a pair of redundant MAPKKKs, whereas the other branch requires the activity of the MAPKKK of the pheromone response pathway, a very surprising finding. One important outcome of the studies with the HOG pathway is that it led to the identification of the first complete His-Asp phosphorelay system in eukaryotes. So far, no His-Asp phosphorelay systems have been identified in mammalian cells. The work carried out by Saito and colleagues provides a model of brilliant genetic detective work and biochemical analysis in the identification and characterization of many of the components of this pathway.
Response to High Osmolarity in S. cerevisiae and S. pombe
Glycerol plays an important role in the adaptation of both budding and fission yeast cells to increased external osmolarity. As both S. cerevisiae and S. pombe cells encounter hyperosmotic conditions, they increase their synthesis of glycerol, which leads to an increased internal glycerol concentration and thus to an increased internal osmolarity, which compensates for the elevated external osmolarity. S. cerevisiae and S. pombe cells unable to produce glycerol are unable to grow on hyperosmotic medium (2, 156). Thus, glycerol appears to be the major osmolyte used by the yeasts. Glycerol accumulation is in part due to increased activity of glycerol-3-phosphate dehydrogenase, encoded by GPD1 in S. cerevisiae and gpd1 in S. pombe (156). This increased activity results from activation of the MAPK cascade. Adaptation to high osmolarity is mediated by the HOG (high-osmolarity glycerol) pathway in S. cerevisiae and the Sty1 (suppressor of tyrosine phosphatase) pathway in S. pombe. In both cases, the MAPK cascade is activated in response to hyperosmolarity and leads to increased expression of a number of target genes.
Activation of the Hog1 MAPK cascade by two different sensors. The Hog1 MAPK cascade (Fig. 2) consists of Ssk2 and Ssk22 (MAPKKK), Pbs2 (MAPKK), and Hog1 (MAPK) (16, 20, 127). Hog1 is activated by phosphorylation by Pbs2 on two residues (Thr174 and Tyr176) that reside in the catalytic domain and are conserved among all MAPKs. Pbs2 is activated by phosphorylation on two residues (Ser514 and Thr518) within the catalytic domain that are also conserved among MAPKKs (see "MAPK cascade nodule and signal transduction" above). Activation of Pbs2 can occur by two different branches (Fig. 2), both sensing hyperosmolarity and each acting independently of the other (127, 128). One branch (the Sln1 branch) involves a His-Asp phosphorelay system; the other (the Sho1 branch) employs a putative transmembrane osmosensor (Fig. 2) (128, 166). The Sln1 branch activates two redundant MAPKKKs (Ssk2 and Ssk22). These MAPKKKs, like other MAPKKKs, contain a large noncatalytic region that has been proposed to play a negative regulatory role in activation of the catalytic domain. A homolog (MTK1) of the Ssk2 and Ssk22 MAPKKKs has been recently identified and shown to mediate activation of the stress pathway in mammalian cells. Given that the similarity of these proteins extends to the noncatalytic regulatory region, it is possible that upstream regulators are also conserved (201).
|
|
Osmosensing involves a multistep phosphorelay system related to the histidyl-aspartyl phosphorelay systems of bacteria. Yeast has coupled two different types of phosphorylation cascades in the high-osmolarity signal transduction pathway. Above, I described phosphorylation through the MAPK cascade, and now I describe phosphorylation in the histidyl-aspartyl (His-Asp) phosphorelay system and how this phosphotransfer affects activation of the MAPK cascade. First, I present a brief overview of His-Asp phosphorelay systems (also known as two-component systems) in bacteria (52).
The His-Asp phosphorelay is widely used by bacteria to sense their external environment and to transduce the signal to the interior of the cell, resulting in altered patterns of gene expression. In this system, phosphate is transferred from a sensor protein to a response regulator (receiver) protein. In particular, the sensor protein contains an autophosphorylating histidine kinase domain, whose activity is modulated by an external stimulus. Activation of this kinase activity results in phosphorylation of a His residue within the kinase domain. The phosphate from this His residue is then transferred to an Asp residue in the receiver protein. The sensor protein may have an extracellular domain and a cytoplasmic domain. The receiver protein is cytoplasmic and transduces the signal. In bacteria, the receiver protein often has a DNA binding domain, so that perception of the signal results in activation of the DNA binding activity (reviewed in reference 52). The phosphorelay system that governs the HOG pathway is complex and consists of three different proteins (Fig. 4): Sln1, Ypd1, and Ssk1 (128, 166). Sln1 contains two putative transmembrane domains that flank an extracellular domain, a cytoplasmic His kinase domain, and a receiver domain. Thus, Sln1 has both a sensor and a receiver domain. His576 in the kinase domain becomes phosphorylated, and the phosphate from His576 is then transferred to Asp1144 in the receiver domain of Sln1 (Fig. 4). The phosphate from Asp1144 is transferred to His64 in a second protein, Ypd1. Lastly, this phosphate is transferred to Asp554 within the receiver domain of the response regulator Ssk1 (Fig. 4) (166). Unlike many of the bacterial response regulators, Ssk1 does not have a DNA binding domain.
|
|
Mutations that turn the pathway on or offuse of epistasis
relationships to order pathway components.
In this section, I
provide some examples of how components of the pathway have been
identified, in some cases by genetic analysis and in others by
inference from nucleotide sequence analysis. Genetic analysis relies on
two key types of mutations: mutations that turn the pathway off and
mutations that turn the pathway on in the absence of stimulus. There is
no good reporter gene (see the next section) for measuring the
activation of the HOG pathway, unlike the situation for the pheromone
response pathway. Activation of the HOG pathway is assayed
biochemically by determining tyrosine phosphorylation of the MAPK Hog1
with commercially available antiphosphotyrosine antibodies on proteins
immobilized on a nitrocellulose membrane after a given treatment (see,
for example, reference 165). Growth on plates with
high osmoticum (1.5 M sorbitol or 0.9 M NaCl) is used in conjunction
with the above assay. This plate assay is also used to screen for
osmosensitive (Osms) mutants in the identification of
pathway components.
N-SSK2 mutation, it was concluded that
PBS2 is downstream of SSK2. Had the result been
the opposite (i.e., no suppression), the conclusion would have been
that PBS2 is most probably upstream. Another constitutive
mutation that results in activation of the HOG pathway is
N-STE11 (165). This constitutive phenotype is abolished by pbs2 mutations, indicating that
STE11 is upstream of PBS2. Constitutive mutations
can also be used to identify unknown downstream components. For
example, sln1 results in constitutivity of the pathway
(and in lethality) (128). Downstream components were
identified by screening for mutants that suppress the lethality of the
constitutive mutation. Mutations in SSK1 (and in other genes
of the pathway) were obtained in this manner.
Redundancy in genes or pathways can be inferred from analysis of the
deletion phenotype of a given gene. For example, it was found that
strains with SSK2 deleted still activated the MAPK Hog1, as
measured by phosphotyrosine phosphorylation. This observation led to
the suspicion that a redundant MAPKKK might exist. Low-stringency Southern blot analysis confirmed this suspicion and led to
identification of SSK22, which is very similar to
SSK2 (although the expression or activity of these genes or
their products may be differentially regulated [see reference
127 for details]). Strikingly, the HOG pathway is
still activated in a strain lacking both SSK2 and
SSK22, and the mutant strain is osmoresistant
(Osmr). Screening for Osms mutants of this
strain led to the identification of additional components of the
HOG1 pathway: SHO1 and STE11
(127, 165).
Stress response element. Heat shock and osmotic stress induce synthesis of an overlapping set of proteins (211, 212; see also reference 77). Genes induced by osmotic stress, for example CTT1 and GPD1, contain a response element in their promoter region that appears to mediate the response to osmotic stress (129, 181). The stress response element (STRE) can also mediate the induction of transcription by other types of stresses, for example heat shock, nitrogen starvation, and oxidative stress, which are independent of the HOG pathway. Because this element mediates both HOG-dependent and HOG-independent induction, the use of STRE-reporter fusions has not proved very useful in analysis of the HOG pathway. Use of a transposon library (177) or of the more recently developed "gene microarrays" (186) should facilitate the identification of Hog1 targets and reporter genes for this pathway.
Response to Stress via the Sty1 MAPK Pathway in
S. pombeCoordination of Multiple Distinct
Outputs in Response to Stress
Fission yeast cells respond to osmotic stress via the Sty1 MAPK pathway (which is also called Spc1 and Phh1) (Fig. 2). Studies of this pathway have led to some important findings which clearly distinguish it from the HOG pathway of S. cerevisiae. First, in contrast to the HOG pathway, which is activated only by hyperosmotic stress, the Sty pathway is also activated by oxidative and heat shock stresses, nutrient limitation, and anisomycin (a protein synthesis inhibitor) (43, 222). Thus, in this respect the S. pombe pathway resembles the p38 and SAPK/JNK stress-activated pathways of mammalian cells (57, 67, 108). Activation of the Sty pathway by multiple stress signals raises the question whether different sensors are used for the different stress signals. Second, the Sty pathway integrates stress sensing with control of mitosis, a very important finding which may shed light on how the extracellular environment regulates mitosis (138, 190). Third, the Sty pathway utilizes a transcription factor with similarity to the transcription factor activated in mammalian cells in response to stress (189, 222). Therefore, the similarity of the pathway to that of mammalian cells extends to the transcriptional activator. Fourth, the Sty pathway links stress signalling with control of sexual differentiation (43, 97, 200). The S. pombe transcriptional activator governs the expression of target genes involved in the stress response and in the initiation of meiosis (189, 200, 222). Thus, the Sty pathway not only regulates stress responses but also integrates this response with two processes fundamental to all eukaryotes: control of mitosis and initiation of meiosis (Fig. 2 and 6).
|
The components of the Sty1 MAPK pathway are homologous to those of the HOG pathway of S. cerevisiae. The MAPK cascade module of the Sty1 pathway (Fig. 2) consists of the MAPK Sty1, which is activated by phosphorylation on the Thr171 and Tyr173 residues by the MAPKK Wis1 (138, 178a, 190). This kinase in turn is activated on Ser469 and Thr473 (178a, 187, 188) by the MAPKKK Wak1 (also known as Wik1 and Wis4). The MAPKKK in turn appears to be activated by Mcs4 (187, 188) (Fig. 2), which has amino acid sequence similarity to Ssk1. It has been proposed that a His-Asp phosphorelay system similar to that regulating the HOG pathway is involved in the response to high osmolarity in S. pombe, although a histidine kinase has yet to be identified (187, 188).
The MAPK Sty1 appears to be downregulated by Pyp2, a tyrosine phosphatase whose expression is induced by stress conditions. It thus appears that Pyp2 participates in a negative-feedback loop that allows restoration of the basal level of Sty1 activity (138, 190). Inactivation of Pyp1, another tyrosine phosphatase that acts on Sty1, has been proposed to be the mechanism by which heat shock activates the Sty1 pathway (178a).A transcription factor with similarity to mammalian ATF2 is the target of the MAPK cascade. A transcriptional activator has not been identified for the S. cerevisiae HOG pathway. In contrast, in S. pombe, the transcriptional activator Atf1 (also known as Gad7) is downstream of the Sty1 MAPK (189, 200, 222) (Fig. 2). Atf1 is a bZIP transcription factor (references 96 and 200 and references therein), highly homologous to mammalian ATF-2 (which is involved in the mammalian stress response). It is phosphorylated in a Sty1- and Wis1-dependent manner and appears to be a direct substrate for Sty1 (189, 200, 222). Several genes are known to be induced by different stress conditions in a Sty1-dependent manner (references 1, 43, 97, 138, 187, 189, 200, and 222 and references therein [detailing the identification and characterization of the genes]): pyp2 (encoding a tyrosine phosphatase), gpd1 (encoding glycerol-3-phosphate dehydrogenase), ctt1 (encoding catalase), fbp1 (encoding fructose-6-phosphatase), ste11 (encoding a high mobility group [HMG] transcription factor), and tps1 (encoding trehalose-6-phosphate synthase). Expression of these genes, not surprisingly, has also been shown to be Atf1 dependent (200, 222), and some evidence exists suggesting that Atf1 directly interacts with ATF-like binding sites in the promoter region of gpd1 (222).
The atf1 gene was identified independently in three different ways: (i) by searching the fission yeast genome for open reading frames with homology to mammalian ATF transcription factors (200), (ii) by screening for genes that on a high-copy-number plasmid suppress the mating defect of sty1 mutants (see below) (189), and (iii) by screening for weak sterile mutants defective in G1 arrest after nitrogen starvation (96). The atf1 mutants, in summary, are Osms, sterile, defective in G1 arrest, and defective in transcription of genes activated by stress conditions. atf1 mutants are not defective in size control at the time of mitosis, an important piece of evidence for proposing that Sty1 controls cell size at mitosis via a different target (Fig. 2) (see the next section (189, 222).Links between the Sty pathway and cell size control at mitosis. Understanding how eukaryotic cells coordinate the response to the extracellular environment and progress through the cell cycle is a key question, about which we have little information. Studies of the S. pombe Sty pathway may provide important insights into how this might occur. In this section, after a synopsis of fission yeast growth and mitotic cycle, I present some of the observations that have led to the proposal that the Sty pathway links the control of cell cycle progression and the response to stress (for more details see references 138 and 190).
Fission yeast cells are cylindrical rods that grow by elongation at the tips. Division occurs when the cells attain a critical cell size, which is constant from cell cycle to cell cycle under the same growth conditions (reviewed in reference 72). A medial septum is laid down, dividing the cell into two equal daughter cells (28). Mitotic initiation is controlled in all eukaryotes by activation of a cyclin-dependent kinase (Cdk), a key regulator of mitosis. At interphase, the Cdk is maintained in an inactive state by phosphorylation carried out by tyrosine kinases. Activation of the Cdk (Cdc2) in S. pombe is triggered by tyrosine dephosphorylation by the Cdc25 phosphatase. Other genes are also involved in control of the timing of mitosis (reviewed in reference 153). Several lines of evidence establish a link between the Sty pathway and control of mitosis. First, the wis1 gene, which encodes a MAPKK, was identified as a dose-dependent initiator of mitosis (215). Overexpression of wis1 causes cells to enter mitosis at a reduced cell size, whereas loss of wis1 causes an elongated phenotype, indicating a delay in entry to mitosis. In addition, wis1 mutant cells are Osms, an important finding tying these different phenotypes to a single gene. Second, loss-of-function mutations in sty1, wak1, and mcs4 all lead to an elongated cell phenotype and to Osms cells (178a, 187, 188). The wis1 sty1 double mutant is as Osms and as elongated as each of the single mutants, suggesting that these genes most probably act in a linear pathway governing the same processes. Third, mcs4 was originally identified as a suppressor of the mitotic catastrophe phenotype of cdc2-3w wee1-50 mutants (references 187, 188, and 190 and references therein). Because mutations in mcs4, wak1, wis1, and sty1 affect not only growth on medium of high osmolarity but also size, it has been proposed that S. pombe cells are able to integrate changes in extracellular osmolarity and control of cell size at the time of mitosis (138, 190). How this is accomplished at the molecular level remains to be determined. In contrast to mutations in the above genes, mutations in atf1 cause osmosensitivity but not an elongated cell phenotype, suggesting that Sty1 controls cell size at mitosis via an output distinct from atf1 (Fig. 2) (189, 200, 222).Identification and order of some of the pathway components.
As in the analysis of the HOG pathway, the use of mutations that
turn the pathway off or on has been extremely useful in ordering the
components of the Sty pathway. One way in which the Sty1 pathway can be
activated constitutively is by expressing genes under the control of
the inducible nmt promoter. In the presence of thiamine, the
promoter is repressed, whereas in its absence, the promoter is
activated, resulting in high-level expression of the gene under its
control. Overexpression of mcs4 in this manner causes
lethality; this lethality can be suppressed by mutations in
wak1, wis1, and sty1, indicating that
these genes are probably downstream of mcs4 (188). The order of wak1 with respect to
wis1 was inferred from the following analysis. As is the
case with the MAPKKK of the HOG pathway, deletion of the N terminus of
Wak1 causes constitutive activation of the pathway and leads to
lethality. Tyrosine phosphorylation of Sty1 in the absence of stimulus
was observed under these conditions and was dependent on a functional
Wis1 protein. The lethality of N-wak1 can be suppressed
by mutations in wis1 but not in mcs4, indicating
that wis1 is most probably downstream of wak1 and
that mcs4 is most probably upstream of wak1
(187). These and other results support the order
Mcs4-Wak1-Wis1-Sty1 (references 178a, 187, and
188 and references therein). Other observations (see references 187 and 188 for
details) have led to the proposal that Wis1 may be activated by an
independent pathway, by analogy to the HOG pathway of budding yeast
(but see reference 178a for an alternative view).
Integration of the response to stress with sexual development. The Sty pathway has proven to be involved not only in regulation of the stress response and mitosis (see above) but also in the initial step leading to sexual differentiation (Fig. 2; also see Fig. 11). Nitrogen starvation, which is required for conjugation and sporulation (see the section on the pheromone response pathway in S. pombe, below), induces the Sty stress response. One consequence of this activation is the transcriptional induction of ste11 (97, 200) (Fig. 2). This gene encodes a transcription factor required for the expression of genes necessary for the initiation of sexual development (199). Thus, an output of the Sty1 pathway, Ste11, subsequently participates in the transcription of genes which then activate the pheromone response pathway (Fig. 2; also see Fig. 11).
The evidence linking the output of the Sty1 pathway with the initiation of sexual differentiation was first suggested by the finding that strains with mutations in components of the Sty pathway exhibited reduced mating and sporulation. On closer examination, these mutants were found to be defective in N starvation-induced G1 arrest and in induction of ste11 mRNA (96, 97, 189, 200, 222). The finding that the 5' regulatory region of ste11 contains putative binding sites for Atf1 suggests a direct role of Atf1 in activating the transcription of ste11. Whether Atf1 acts alone or in conjunction with another ATF-like protein, Pcr1, which is also required for G1 arrest and ste11 expression, remains to be determined (for details, see references 96 and 200). The discussion of the S. cerevisiae HOG and S. pombe Sty pathways has attempted to summarize our current knowledge of the response to high osmolarity in the yeasts. Comparison of these pathways shows that structurally related MAPK cascades can be used to respond to only one stimulus, as in the HOG pathway, or to multiple stimuli, as in the Sty pathway. More importantly, studies on the Sty pathway have shown that the cell can integrate its response to external stimuli with critical processes in the life cycle of an organism, such as mitosis and meiosis (Fig. 6). The similarities of the components of these pathways make it likely that homologs are to be found in other fungi, where they might regulate a variety of processes. The relatedness of the components of the HOG and Sty pathways should allow a rational design of degenerate primers for the candidate gene approach to identify the desired genes in the organism of choice. As the studies with nik-1 in N. crassa show, osmosensing pathways can be important in the regulation not only of hyphal growth but also of hyphal morphology (3, 182).PKC Pathway in S. cerevisiae and Response to Low Osmolarity
In contrast to the HOG pathway, which responds to hyperosmolarity, the PKC pathway is activated by low osmolarity. It is also activated in response to a variety of stimuli: nutrient sensing, thermal stress, and pheromones (38, 40, 95, 136) (Fig. 7). It is thought that a major role of the PKC pathway in response to these stimuli is to maintain cell integrity by controlling cell wall assembly and perhaps membrane assembly.
|
Changes in cell wall composition can occur in response to growth medium, pheromones, cell fusion, cell cycle, and, in the case of pathogenic fungi, contact and growth within their host (136, 164, 230; see also reference 34). During apical growth of a yeast bud or a hypha in the cell cycle, the cell wall is in a dynamic state of change as new material is added at the growing point and subsequently modified to produce a structure capable of sustaining mechanical and chemical stress (reviewed in references 24 and 34). These modifications of the cell wall in response to diverse conditions entail activation of cell wall-synthesizing enzymes resident in the cell membrane and vectorial transport and exocytosis of vesicles that carry other wall and membrane components (reviewed in reference 34). The inability of a cell to modify its cell wall accordingly may result in a fragile cell wall and may lead to cell lysis, misshapen cells, or altered patterns of growth (for example, altered branching patterns or septum deposition).
Because one of the functions of the PKC pathway is to control the expression of genes encoding cell wall components and possibly also to control the vectorial transport of vesicles that may contain other components essential for cell integrity, this pathway is likely to be a major player during bud formation and hyphal extension. Studies of the PKC pathway in budding yeast should provide insights into how different input signals are integrated and mediate cell integrity.
Some notable features of the PKC pathway are as follows: (i) a small GTP binding protein (Rho1) controls the activity of the Pkc1 protein and also of glucan synthase, an enzyme involved in the synthesis of a major structural component of the fungal cell wall; (ii) a homolog of a phosphatidylinositol kinase regulates the activity of the Rho1 protein, perhaps linking phospholipid metabolism with cell wall synthesis and integrity in yeast; and (iii) a recently identified presumptive integral membrane protein may act as one of the sensors for the pathway.
PKC MAPK cascade and its activation. The MAPK cascade module that mediates the transduction of the signal generated by low osmolarity and heat stress consists of the MAPK Mpk1, two redundant MAPKKs, Mkk1 and Mkk2, and the MAPKKK Bck1 (Fig. 7) (38, 88, 89, 114, 115, 136, 206). The proposal for sequential activation by phosphorylation of the MAPK cascade is based on in vivo epistasis analysis and on structural relatedness to kinases in other pathways for which in vitro function has been established. The MAPK Mpk1 is tyrosine phosphorylated and activated in response to heat shock and hypotonic conditions in an Mkk1- Mkk2-, Bck1-, and Pkc1-dependent manner (40, 95, 230). Mpk1 tyrosine phosphorylation increases as osmolarity decreases from isotonic conditions. In contrast, as osmolarity increases, Hog1 tyrosine phosphorylation increases. Thus, these two MAPKs are activated by opposite osmolarity conditions (40).
(i) Activation by Pkc1. The MAPK cascade is activated by Pkc1 (Fig. 7), a serine/threonine protein kinase, although the mechanism of this activation is not known. Pkc1 contains several domains: a catalytic domain, a putative Ca2+ binding domain (C2 domain), a putative diacylglycerol (DAG) binding domain (C1 domain), and a pseudosubstrate domain. Thus, budding yeast Pkc1 resembles mammalian isoforms that require phospholipid, Ca2+, and DAG as cofactors for activation (118, 152). Mammalian protein kinase C enzymes (PKCs) govern cell growth, proliferation, differentiation, and other processes (reviewed in references 44 and 150). In mammalian cells, PKCs respond to extracellular signals through receptor-mediated hydrolysis of phosphatidylinositol-4,5-bisphosphate to diacylglycerol (DAG) and inositol-1,4,5-triphosphate (IP3). DAG serves as a second messenger to activate PKC, and IP3 functions to mobilize Ca2+ from intracellular stores (reviewed in reference 46). The pseudosubstrate domain is conserved in PKCs from yeast to mammalian cells and is proposed to maintain the PKCs in an inactive state in the absence of inducing signal (reviewed in reference 44). The fact that a mutation (Pkc1R398P) resulting in constitutive activation of yeast Pkc1 maps to the pseudosubstrate region supports this contention (152). Pkc1 is activated by Rho1 (see the section on Rho1 regulation of Pkc1 and glucan synthase, below).
Deletion of any of the genes encoding components of the MAPK cascade (bck1, mkk1 mkk2, or mpk1)
results in the same phenotype: cell lysis at elevated temperature,
which is osmotically remedial. This phenotype is also exhibited by
mutants defective in the HCS77 gene (65) (see
below). Because these components are needed only at 37°C, it is
likely that a partially redundant pathway operates at other
temperatures; perhaps this pathway is the other branch controlled by
Pkc1 (Fig. 7) (see below). In contrast to this temperature-sensitive growth defect, PKC1 and RHO1 (see below) are
essential for growth at all temperatures. pkc1 mutants
proliferate only in osmotically stabilized medium; they undergo rapid
lysis after transfer to medium lacking osmotic stabilizer (117,
158). Because deletion of PKC1 causes a more severe
phenotype than does deletion of MPK1, it has been proposed
that Pkc1 governs a branched pathway (Fig. 7) (115), but
little is known of this branch. Because rho1 cannot be
osmotically stabilized, Rho1 has been inferred to govern targets other
than Pkc1 (Fig. 7) (152) (see below).
(ii) Activation by pheromones.
Mpk1 appears to be
tyrosine phosphorylated and activated in response to pheromones (Fig.
7) (230). This phosphorylation is dependent on Bck1 and,
surprisingly, also on Ste20, a protein kinase that activates the MAPK
cascade of the pheromone response pathway (see the section on the
pheromone response pathway in S. cerevisiae, below).
Phosphorylation was observed 1 h after treatment with pheromone
and was not dependent on Ste12. Pheromones induce the formation of a
mating projection exhibiting highly polarized growth. Since Mpk1 has
been implicated in polarized growth (proper chitin deposition,
organization of cortical actin patches, and vectorial transport of
vesicles), it is possible that pheromone induction of Mpk1 ensures cell
wall integrity during projection formation (136, 230). In
this context, it is worth noting that BCK1 mutants were
identified in a synthetic lethal screen with mutants defective in
SPA2, a gene required for projection formation during mating
(38). The PKC pathway is necessary during projection
formation but not during cell fusionan activated allele of Pkc1
blocks cell fusion (164). During cell fusion, localized degradation of cell walls occurs in the area of cell-cell contact. This
degradation is essential to allow the fusion of cellular membranes to
form a zygote. One possibility is that the PKC pathway is downregulated
at this stage to allow cell fusion (see reference 164 for details).
Rho1 regulates Pkc1 and glucan synthase.
(i)
Activation of Pkc1.
Rho1 belongs to the family of small GTP
binding proteins which includes the Rho, Rac, and Cdc42 subfamilies.
These proteins have GDP- and GTP-bound states and act as molecular
switches regulating a variety of cellular processes (reviewed in
references 172 and 203). The
switch from one state to the other is controlled by two types of
proteins: a guanine exchange factor (GEF), which promotes the
transition from the GDP-bound form to the GTP-bound form, and a
GTPase-activating protein (GAP), which promotes GTP hydrolysis and
hence the transition from the GTP state to the GDP state. The GTP-bound
form is usually the active form and interacts with target proteins.
(Examples are known, however, in which both GTP- and GDP-bound forms
have different functions [159].) Rho has been proposed
to be involved in reorganization of the actin cytoskeleton in mammalian
cells and, through this process, to affect cell morphology, motility,
and cytokinesis (reviewed in references 172 and
203). In S. cerevisiae, Rho1 is localized at sites of active growth or secretionthe presumptive bud site, the
bud tip, and the neck regionand has been proposed to play an
important role in bud formation. Rho1 localization coincides with
localization of actin patches during the cell cycle (229). Actin is proposed to be involved in the transport of vesicles to the
actively growing regions. Whether Rho1 is involved in actin reorganization in yeast is not known at present. The similarity of
phenotype of both pkc1(ts) and
rho1(ts) mutants and their suppressibility by 1 M
sorbitol led to the suggestion that both RHO1 and
PKC1 act in the same pathway.
rho1, although it
suppresses the rho1(ts) mutation, it has been
proposed that Rho1 has other substrates in addition to Pkc1
(152).
(ii) Rho1 activates glucan synthase.
Yeast cell walls
appear to be layered, with an inner, electron-transparent layer
containing mainly glucan polymers and a fibrillar, electron-dense outer
layer consisting mainly of mannoproteins. 1,3-
-Glucan polymers and
mannoproteins are the major structural components of the yeast cell
wall (reviewed in references 24, 34, and
87). In the filamentous Ascomycetes and in the
Basidiomycetes, in addition to 1,3--glucan and mannoproteins, chitin
is another major structural component (reviewed in reference
192). Synthesis of 1,3--glucan polymers is
mediated by 1,3--glucan synthase (GS), a membrane-bound enzyme whose
activity is stimulated by GTP. GS catalyzes the transfer of a glucosyl
residue from UDP-glucose to a growing chain of 1,3--linked glucosyl
residues (141; reviewed in references
24 and 87). Two genes,
FKS1 and FKS2, encoding components of the
catalytic moiety of GS have been identified in S. cerevisiae. Deletion of both FKS1 and FKS2
is lethal, whereas deletion of either is not, although the single
mutants are very sensitive to cell wall inhibitors such as
echinocandin. Both Fks1 and Fks2 exhibit a high degree of similarity at
the amino acid level: 16 putative membrane-spanning domains, of which 6 comprise a block separated from the other 10 by a stretch of
hydrophilic amino acids (50, 135). Because their structure
resembles that of ATP binding cassette (ABC) transporters of bacteria
(reference 50 and references therein), it is
hypothesized that the glucan chain is extruded into the periplasmic
space as it is synthesized (51).
-glucans in two ways: (i) by activation of the PKC pathway, which
regulates the synthesis of the catalytic subunit of GS; and (ii) by
direct activation of GS enzymatic activity (51, 84) (see
below).
Targets of the PKC pathway. The direct target of the PKC MAPK cascade appears to be a transcriptional activator (Rlm1) that may regulate the expression of genes for cell wall biosynthesis. It is also possible that additional targets exist for this pathway.
(i) Rlm1, a transcriptional factor downstream of Mpk1. Rlm1 is a member of the MADS box of transcription factors, of which S. cerevisiae Mcm1 and mammalian serum response factor (SRF) are also members (218). The DNA binding domain of Rlm1 is most similar to that of mammalian MEF2 and appears to bind the same consensus sequence as MEF2 (47). The yeast genome contains a homolog of Rlm1, Smp1, which recognizes an extended version of the consensus recognized by Rlm1. The two proteins can form heterodimers (47). The C-terminal region of Rlm1, which may be the transcriptional activation domain, appears to be directly phosphorylated by Mpk1 in vivo and in vitro, suggesting that Mpk1 modulates the activation domain of Rlm1 (47, 217). Deletion of RLM1 or of SMP1 does not result in the cell lysis phenotype characteristic of deletion of the components of the PKC pathway. One possibility is that Mpk1 exerts its effects via targets in addition to Rlm1 and Smp1 (for details, see references 47 and 217).
(ii) Genes for cell wall biosynthesis.
The expression
of several genes involved in cell wall biosynthesis is cell cycle
regulated in a SWI4- and SWI6-dependent manner and peaks at the G1/S boundary, which coincides with active
apical growth and extensive wall remodelling (84). These
genes are FKS1, KRE6, MNN1,
VAN2, CSD2, and GAS1, which encode,
respectively, a subunit of GS, a protein for 1,6--glucan synthesis,
proteins involved in mannosylation, a protein involved in
glycosylation, chitin synthase III, and a glycosylphosphatidylinositol
(GPI)-anchored membrane protein (reference 84 and
references therein). Not surprisingly, these genes contain cell cycle
regulatory sites in their 5' regions (84). Pkc1 is not
required for this cell cycle regulation but is required for a high
constitutive level of expression of FKS1, CSD2,
MNN1, KRE6, and GAS1 throughout the cell cycle. It has been proposed that the PKC pathway and Swi4-Swi6 regulate the synthesis of these genes in a coordinated manner and that
this might explain the synthetic lethality observed for swi4 or swi6 and components of the PKC
pathway (84).
-glucan synthesis; KTR2, encoding mannosyltransferase;
HSP150, required for cell wall integrity; FLO1,
which governs flocculation; AFR1, whose product is involved in pheromone-induced morphogenesis; and FKS1 (see above)
(reference 47 and references therein). Of these
genes with MEF2 consensus sites, only FKS1 is regulated by
Pkc1 (84). It remains to be determined whether the others
are also regulated by Pkc1. It is possible that Pkc1 regulates their
expression via another unidentified transcription factor.
The work of Igual et al. (84) and others, indicating that
pkc1 mutants have an altered cell wall organization due to
lowered 1,3--glucan, 1,6--glucan, and mannan content (158,
176), provides key evidence for the role of the PKC pathway in
cell integrity by regulation of cell wall biosynthesis. The role of
Pkc1 in cell wall integrity has been argued largely on the basis of the
cell lysis phenotype exhibited by strains with mutations in the
pathway. Although suggestive, it has never been convincingly
demonstrated whether lysis precedes or follows death. Cells can lyse
for a number of reasons, some of which, of course, are due to cell wall defects.
Hcs77, a putative receptor that senses membrane
stretch.
HCS77 encodes a protein of 378 amino acid residues
with a single putative transmembrane domain and an N-terminal signal
sequence (65, 155). A number of observations indicate that
it functions in the PKC pathway. Deletion of HCS77 results
in a phenotype that is similar to the phenotype observed for deletion
of components of the PKC pathwaya temperature-dependent cell lysis
phenotype that can be remedied by osmotic stabilizers. hcs77
bck1 and hcs77 mpk1 double mutants exhibit the
same phenotype as the single mutants, consistent with the view that
they act in the same linear pathway (65). Of particular
importance is the observation that heat induction of Mpk1 activity was
reduced in the hcs77 mutant strain. Taken together, these
results suggest that Hcs77 may be an upstream regulator of Pkc1.
Because the phenotype of hcs77 is not as severe as that
of pkc1, it can be argued that Pkc1 can be activated in
other ways.
|
PHEROMONE RESPONSE MAPK CASCADE FOR MATING, MEIOSIS, AND FILAMENTOUS GROWTH
|
TopPreviousNextReferences
|
|---|
Pheromone Response Pathway in S. cerevisiae
In this section I first describe the pheromone response pathway of
S. cerevisiae and then that of S. pombe. The
machinery used for the responsereceptors, pheromones, heterotrimeric
G protein, and MAPK cascadeis highly conserved, but some of the components are used differently. In particular, G
transmits the
signal to downstream components in budding yeast whereas G
performs
this task in fission yeast. Inputs other than the pheromones can
modulate activity of the pathway in one of the yeasts. Because pheromones and receptors (and presumably a conserved response pathway)
regulate filamentous growth in Basidiomycete fungi, it is likely that
similar machinery is used by these fungi in their response to
pheromones. Additional inputs are likely to be required to modulate the
complexity of the developmental pathway leading to filamentous growth.
The pheromone response pathway of S. cerevisiae mediates cell-cell interactions during mating. This pathway has been intensively studied for many years and is one of the best-understood signalling pathways in eukaryotes. Studies with the pheromone response pathway of budding yeast have provided a framework for understanding how mitogenic factors regulate cell cycle progression in mammalian cells. An overview of this pathway follows (Fig. 9). (i) Peptide pheromones secreted by cells interact with seven-transmembrane receptors and initiate the response. (ii) The receptors interact with a heterotrimeric G protein that transmits the signal to downstream components. (iii) Partially redundant MAPKs mediate the activation of a transcription factor. (iv) One of the MAPKs phosphorylates a cyclin-dependent kinase inhibitor (CKI), leading to cell cycle arrest. (v) A component of the response pathway appears to act as a scaffold that brings together the MAPK cascade components and may prevent cross talk between this and other pathways. (vi) Many of the target genes for this pathway are known and include genes necessary for cell and nuclear fusion and for cell cycle arrest.
|
MAPK cascade and Ste5 scaffold. The MAPK cascade (Fig. 9) consists of the MAPKKK Ste11, which phosphorylates and activates the MAPKK Ste7 on two residues conserved among all MAPKKs. Ste7 in turn phosphorylates and activates the redundant MAPKs Fus3 and Kss1 on conserved Thr and Tyr residues (56, 59, 122, 148, 235).
Downstream of the MAPKs is the transcriptional activator Ste12 (Fig. 9). Ste12 governs the expression of many genes in the pheromone response pathway and also genes for cell and nuclear fusion. It binds to a pheromone response element (PRE) located in the 5' regulatory region of target genes (reviewed in references 107 and 132). Because Ste12 is phosphorylated by both MAPKs, it was proposed to be the direct target of the MAPKs (54, 81, 194). Studies of the activation of Ste12 by the MAPKs has revealed new levels of complexity: additional components are involved in the interaction of the MAPKs with Ste12. The proteins encoded by two recently discovered genes, RST1 (DIG1) and RST2 (DIG2), appear to act as inhibitors of Ste12 activation in the absence of pheromone. Both Fus3 and Kss1 interact with these proteins and phosphorylate them. Ste12 also interacts with Rst1 and Rst2 (37, 204). Rst1 and Rst2 are proposed to form a complex with Ste12 at Ste12 target sites, preventing transcriptional activation. Upon pheromone stimulation, the MAPKs phosphorylate Rst1, Rst2, and Ste12, resulting in dissociation of the complex and allowing Ste12 to activate transcription (Fig. 9) (see reference 37 for other models). It must be noted that the sites phosphorylated in Ste12 are not known, nor has the biological significance of this phosphorylation been determined, although it correlates with transcriptional activation (see references 81 and 194 for details). Fus3 and Kss1 have been considered to be partially redundant MAPKs for transcriptional induction and mating but not for cell cycle arrest. Of the two MAPKs, only Fus3 phosphorylates Far1 (Fig. 9). This phosphorylation of Far1 regulates its association with the Cdk, causing cell cycle arrest in G1 (Fig. 9) (162). Recently, it has been proposed that Fus3, and not Kss1, is the MAPK for this pathway. A kinase-deficient point mutation of FUS3 has a severe defect in mating, indicating that Kss1 cannot substitute for Fus3 function when Fus3 protein is present, albeit in an inactive form (see reference 125 for details). Kss1 can supplant Fus3 only when Fus3 is absent due to deletion of the FUS3 gene (125). The mechanism by which the MAPK cascade is activated is not well understood and remains an intensive area of research. It might involve Ste20 or Ste5 or both (Fig. 9). The role of Ste20 will be discussed in a separate section (see below). The role of the Ste5 protein remained enigmatic for many years, even though it had been identified two decades ago (124). Epistasis analysis placed it after the G protein and before the MAPK cascade components (for details, see references 71, 104, and 112). STE5 codes for a protein with a LIM-like motif, which appears to mediate protein-protein interactions in other systems (112). Dimerization of Ste5 has been proposed to result in its activation, and the LIM motif, together with other domains, may promote Ste5-Ste5 interactions (227). Ste5 also has Pro-rich regions on either side of the LIM motif, which may interact with SH3 domain-containing proteins (reviewed in reference 53). The work of several groups, using the two-hybrid system and immunoprecipitation, led to several important findings on the role of Ste5 (32, 131, 167). First, Ste5 interacts with all of the components of the MAPK cascadeSte11, Ste7, Fus3, and Kss1. Second, each of the MAPK
components interacts with a different region of Ste5. Third, Ste5
interacts with the amino-terminal region of Ste11, an autoinhibitory region in all MAPKKKs. These and other observations led to the proposal
that Ste5 acts as a scaffold to bring the MAPK cascade components
together to promote sequential phosphorylation during activation of the
pathway and also to facilitate attenuation of the response by Fus3
(reviewed in reference 53) (Fig. 9). Because the
MAPK cascade components of the pheromone response pathway are
structurally very similar to those of other pathways that coexist in
the same cell, it has been suggested that another role of Ste5 is to
prevent cross talk between pathways by confining the components of the
pheromone response MAPK cascade in a complex. For example, such a
complex may prevent Ste11, Ste7, and Fus3 from activating other
pathways inappropriately (reviewed in reference 73).
It is anticipated that other MAPK cascades will have proteins analogous
or homologous to Ste5. Pbs2, the MAPKK of the HOG pathway, has been
proposed to act as a scaffold (165) (see the section on
response to high osmolarity in S. cerevisiae and S. pombe, above).
Attenuation of the pheromone response may involve phosphorylation of
Ste7 and Ste5 by Fus3 (56, 59, 104) and also
dephosphorylation of the MAPK Fus3 by the phosphatase Msg5 and other
phosphatases (49, 231). In addition, the receptors and the
Sst2 protein play a role in attenuation of the response (see below).
Upstream of the MAPK cascade: pheromones, receptors, and heterotrimeric G protein.
(i) Pheromones.
Two types of
peptide pheromones exist in S. cerevisiae: -factor (13 amino acid residues), which is secreted by cells and is encoded by
two genes, MF1 and MF2, and
a-factor (12 amino acid residues), which is secreted by
a cells and is encoded by two genes, MFa1 and
MFa2 (reviewed in references 74, 107, and
132). Purified -factor added to a
cells induces the same changes as when a and cells are
cocultured: growth inhibition and formation of a mating projection
(shmoo). Growth inhibition is due to arrest in the G1 phase
of the cell cycle. Other assays have shown that upon pheromone
treatment, expression of several genes is induced, including the
receptor and pheromone precursor genes, genes for cell fusion, and
genes for nuclear fusion (reviewed in references 107
and 132). Unlike -factor, the a-factor
precursor is modified at its C terminus by carboxymethylation and
farnesylation (reviewed in references 107 and
132). The farnesyl moiety is found in many
eukaryotic proteins and is proposed to target the proteins to the
membrane (35). Both and a cells contain the
genes for the different pheromones and the different receptors, but
expression of the genes is cell type specific, governed by regulatory
proteins encoded by the mating-type locus (MAT) (reviewed in
reference 74). In contrast, in the filamentous
Basidiomycetes, the pheromone precursor and receptor genes are encoded
by the mating-type loci themselves (reviewed in references 6,
25a, and 210).
-factor-like peptides. Thus, purified pheromone may not be as
readily available for the types of experiments that have been so useful
in yeast with commercially available -factor.
(ii) Receptors and heterotrimeric G proteins.
The
receptors in both a and cells are of the
seven-transmembrane type. The receptor for a-factor is
encoded by STE3, and that for -factor is encoded by
STE2 (reviewed in reference 74). There is
little similarity between the amino acid sequence of these receptors,
although there is structural conservation. The third cytoplasmic loop
of the -factor receptor has been implicated in pheromone
discrimination, receptor activation, and internalization (21,
197; see also reference 18).
Phosphorylation of the C-terminal tail mediates adaptation to the
pheromone response, and ubiquitination governs internalization of the
receptor (31, 75, 178; reviewed in reference
110).
, G, and G subunits, encoded by the
GPA1 (SCG1), STE4, and
STE18 genes, respectively (reviewed in references
107 and 132). Both Ste4 and Ste18
precursors have a CAAX box at their C terminus (reviewed in references
107 and 132), a hallmark for
isoprenylation. Activation of the receptor results in exchange of GDP
for GTP in the G subunit and concomitant dissociation of the
heterotrimeric G protein into G-GTP and G subunits (reviewed in references 19, 147, and 171).
G is the activator of the downstream components (reviewed in
reference 73): a null mutation of GPA1
results in constitutive activation of the pathway and lethality due to
cell cycle arrest, whereas ste4 or ste5
results in a nonmating phenotype. A key observation is that double
mutants, for example gpa1 ste4, behave as
ste4, indicating that G is the activator. Binding
of G to G prevents activation by G in the absence of
stimulus (reviewed in references 73, 110, and
132). The SST2 gene is required for
adaptation to the response: sst2 mutations cause
hypersensitivity to the pheromones (45, 48). It is
hypothesized that Sst2 is a GAP for G-GTP, as is now known to be the
case for some members of the RGS family of proteins in other eukaryotes
(13; reviewed in references 101 and 191).
A very important question remaining in studies of the pheromone
response pathway is the mechanism by which G activates downstream components and the molecular nature of the signal. Ste4 and Ste5 appear
to interact as assayed by two-hybrid analysis and immunoprecipitation. The first 214 amino acid residues of Ste5 appear to be sufficient for
this in vivo interaction, although whether the interaction is direct
remains to be determined (221). Such an interaction might be
important for translocation of Ste5 to the membrane, where G
resides. Other work suggests that Ste5 and Ste20 interact, but again it
is not known if this interaction is direct (116). One
possibility is that G transmits a signal to both Ste5 and Ste20
(Fig. 9). Alternative possibilities exist, and future experiments should clarify these interactions.
Ste20, a p65PAK protein involved in mating. A key link of the MAPK cascade with upstream elements may be the Ste20 protein, which was placed upstream of the MAPK cascade and downstream of the G protein by epistasis analysis (reviewed in reference 110). Because it is a kinase (109, 113, 161, 169) (see below), an attractive possibility is that it activates Ste11 by phosphorylation. In vitro studies indicate that Ste20 phosphorylates Ste11 but whether this interaction is relevant in vivo remains to be determined (224).
Ste20 is a serine/threonine protein kinase of the p65PAK family found in different eukaryotic organisms and shown to be activated in vitro by GTP-bound Cdc42, a member of the Rho family of small GTP-binding proteins (reviewed in references 22 and 184). Ste20, like many members of this family, contains a C-terminal catalytic domain and an N-terminal noncatalytic region, within which is a conserved motif, the Cdc42/Rac interactive binding motif (CRIB), necessary for binding by activated Cdc42 (reviewed in reference 22). Activation of p65PAK proteins may mediate the role of Rho proteins in governing the reorganization of the actin cytoskeleton in response to diverse stimuli (184). This prompted an investigation of whether binding of Cdc42 to the CRIB site of Ste20 is responsible for activation of the pheromone response MAPK cascade (109, 161, 193, 233) and for the morphological changes that ensue, which involve reorganization of the actin cytoskeleton. The role of Cdc42 in the pheromone response pathway has been definitively tested by examining the phenotype of STE20 mutants that lack the Cdc42 binding site (109, 161). These mutants exhibit normal transcriptional induction, mating projection formation, and G1 arrest. Thus, Cdc42 binding to Ste20 is not necessary for early steps in the pheromone response. Given that Cdc42 binds Ste20 in vitro and in vivo and that the CRIB site is necessary for such interaction, what is the role of this interaction? One possibility is that association of Cdc42 with Ste20 has a role in cell-cell contact during fusion, as inferred from the fact that mutants with deletion of the CRIB site show a reduced frequency of zygote formation (109, 161). This behavior is not due to defects in actin cytoskeleton organization, inability to orient toward a pheromone source, or inability to form mating projections, which occur normally in the mutants. Because Cdc42 binding to Ste20 is necessary for localization of Ste20 at the shmoo tip, one possible explanation for a defect in cell-cell contact is that Ste20 is necessary for polarized secretion of components necessary for adhesion. These studies have clarified much about the role of Ste20 in the pheromone response pathway. Nonetheless, it remains to be determined how Ste20 is activated. It has been suggested that p65PAK proteins may be activated by G-protein-linked receptors in a Rho-independent manner (reviewed in reference 184). It is thus possible that G activates Ste20 by an as yet
unknown mechanism. Because the noncatalytic region of Ste20 appears to
inhibit activation of the catalytic domain (109, 169), one
possibility is that this region is the target of G (reviewed in reference 110).
Identification of the components of the pathway. Most of the components of the pathway have been identified by simple genetic screens and selections in combination with simple assays for the pathway. The "halo" assay tests growth inhibition in response to pheromones: strains that are sensitive cannot grow around the source of pheromone and form a clear zone or halo of no growth, whereas resistant strains produce no zone of inhibition (reviewed in reference 74). Transcriptional activation of the pathway is assayed by measuring the level of induction of FUS1-lacZ, a reporter gene which is highly induced by pheromone treatment (reviewed in references 107 and 132). Elucidation of the order of the components relied on the use of constitutive mutations which activate the pathway in the absence of pheromone and mutations which turn the pathway off and, more recently, on the use of two-hybrid analyses and biochemical techniques.
Because-factor causes growth inhibition of a cells,
isolation of mutants resistant to this growth inhibition led to the
identification of STE2, STE4, STE5,
STE7, STE11, STE12, STE18,
and FUS3 (also identified as a gene required for cell
fusion) (27, 55, 70). FAR1 was identified as a
mutation conferring -factor transcriptional induction, in contrast
to other -factor-resistant mutants, which block transcriptional
induction (28). A subset of these components was also
identified as mutations that confer a nonmater phenotype:
STE2, STE3, STE4, and STE5
(124). Many of the genes involved in a-pheromone
biosynthesis were also identified as mutations that result in a
nonmater phenotype: STE6, STE14, and
STE16 (reviewed in reference 132). The
gene encoding G (GPA1/SCG1) was identified because its
expression on a high-copy-number plasmid confers -factor resistance.
It was also identified by hybridization with a rat G gene as a probe (reviewed in references 107 and
132).
Constitutive mutations in STE11 allowed the ordering of
STE11 with respect to STE7 and FUS3
but left its relationship with STE5 ambiguous, since the
STE11 constitutive allele suppresses the FUS1
transcriptional defect of ste5 but not the mating defect (25, 198). Constitutive mutations in STE5 allowed
the ordering of STE5 with respect to G (encoded by
STE4 and STE18) but left its position with
respect to STE11 ambiguous (71). The use of the
two-hybrid system led to a definitive explanation of these discrepancies as already described (32, 131, 167).
Pheromone Response Pathway in S. pombe
In contrast to S. cerevisiae, in S. pombe the pheromone response pathway is used not only for mating but also for initiation of meiosis, an observation that is highly relevant to Basidiomycetes, where pheromones and receptors are necessary for postfusion events. The pheromone response pathways of the two yeasts use essentially the same machinery, but as we shall see, one of the components is used differently.
Several features of the S. pombe pheromone response pathway
distinguish it from the S. cerevisiae pathway: first, two
inputs appear to be important for activation of the MAPK cascade, a
G-protein-coupled receptor and the Ras1 protein. Second, G rather
than G is the activator of the pathway. Third, nitrogen
starvation is essential for activation of the pathway. It induces the
expression of a transcriptional activator (Ste11) essential for the
transcription of many genes necessary for the pheromone response,
including the mating-type genes, which, unlike the MAT genes
of S. cerevisiae, are not fully expressed during vegetative
growth.
Before describing the pheromone response pathway in fission yeast, I will give a brief account of the different mating types and the regulators that govern cell type specificity and initiation of meiosis (see Table 1).
|
Haploid cells of S. pombe are of two mating types: minus
(h
) and plus (h+), and
they produce M and P pheromones, respectively, upon nitrogen starvation
(reviewed in references 228 and
228a). The M-factor precursor is encoded by three
genes: mfm1, mfm2, and mfm3. M factor, like a-factor, is farnesylated and carboxymethylated
(100; reviewed in reference 41).
The P-factor precursor is encoded by the map2 gene and is
structurally similar to the -factor precursor of S. cerevisiae (85). In response to mating pheromones,
cells produce a short conjugation tube and fuse to form a zygote, which immediately undergoes meiosis and sporulation. Thus, meiosis is tightly
coupled to mating (reviewed in references 228 and
228a).
The mat genes control mating type and also entry into
meiosis. M cells have the matM allele with two genes,
matMm (matMi) and matMc. P cells have
the matP allele with two genes, matPm (matPi) and matPc (reviewed in references
228 and 228a). matMc and matPc are expressed constitutively at a low level and
become fully induced upon nitrogen starvation (see the section on
stepwise induction of mating and meiosis by nitrogen starvation and
pheromones, below). They are required for expression of the pheromone
and receptor genes. In contrast, matPm and matMm
are expressed only under nitrogen starvation, become fully induced by
pheromones, and are absolutely required for initiation of meiosis
(199, 223, 228a) (see the section on stepwise induction of
mating and meiosis by nitrogen starvation and pheromones, below).
matPm and matMm act together to induce the
expression of mei3, a positive regulator of meiosis, which
functions by inhibiting an inhibitor of meiosis (Ran, also called Pat):
Mei3 | Ran | Mei2 
meiosis (137; reviewed in reference 228a). The requirement for the
combinatorial activity of Pm and Mm in the regulation of meiosis is
similar to the requirement of a1-2 for meiosis in
S. cerevisiae.
MAPK cascade components.
The MAPK cascade consists of
the Byr2 MAPKKK, the Byr1 MAPKK, and the Spk1 MAPK (64, 145, 205,
213) (Fig. 10). These kinases are
presumed to act sequentially (see reference 149 for
details). As in S. cerevisiae, binding of pheromones to the
receptors results in dissociation of the heterotrimeric G protein into
G-GTP and G subunits. G transmits the signal to downstream
components. The observation that led to this conclusion is that
deletion of the gene encoding G (gpa1) results in a
nonmating phenotype (154). Both G and Ras1 are needed for
activation of the MAPK cascade (reference 85 and
references therein; reviewed in reference 79), and
the signal that they transduce converges on the MAPKKK Byr2 (Fig. 10).
Ras1 interacts with Byr2, but the mechanism by which this interaction
leads to activation is unknown (134). The input from G
and Ras1 may be coordinated by the pheromones, as suggested by the fact
that ste6, encoding the putative GEF for Ras1, is
transcriptionally induced by both nitrogen starvation and pheromones
(80).
|
Stepwise induction of mating and meiosis by nitrogen starvation and pheromones. In contrast to S. cerevisiae, S. pombe initiates sexual development only under nitrogen starvation (reviewed in references 228 and 228a). Expression of the components of the pheromone response pathway in S. pombe occurs in several steps, an initial step in response to nitrogen starvation, a second step involving cell-type-specific regulatory proteins, and a third step in response to pheromones and the pheromone response pathway (Fig. 11) (99, 223). The following description is a synthesis of work by different groups and may reflect some simplification.
|
, slight
induction; pher, pheromones; N-starv, nitrogen starvation. See the text
for details.
diploid cell (reviewed in reference 74), S. pombe
h+/h diploids transcribe these
genes (85, 202).
The role of cyclic AMP (cAMP) in sexual development has been omitted
from the above discussion for various reasons. Briefly, high levels of
cAMP (and thus of cAMP-dependent protein kinase, PKA) inhibit sexual
development whereas low levels of cAMP (and PKA) promote sexual
development. Nitrogen starvation results in lowered cAMP levels. It
appears that a trimeric G protein monitors nutritional conditions and
may regulate the activity of adenylyl cyclase and thus cAMP and PKA
levels. The mechanism by which cAMP and PKA regulate sexual development
remains to be determined (reviewed in reference
228a).
In U. maydis, Prf1 is also a member of the HMG family of
proteins and appears to recognize a site similar to that recognized by
Ste11 of S. pombe. prf1 mRNA is apparently induced by
pheromones, and Prf1 in turn regulates the expression of pheromone
precursor and receptor genes and also of the genes at the b
locus (69). Whether Prf1 is the direct target of a MAPK is
not known.
Ras1 has a dual regulatory function: activation of the pheromone MAPK cascade and activation of a polarity and cell morphology cascade. An important feature of Ras in mammalian cells is connecting the outputs from diverse types of receptors to MAPK cascades. This connection involves adaptor proteins such as Grb2, which recruits Sos (the exchange factor for Ras) to the receptor, leading to activation of Ras (reviewed in reference 133). Ras-GTP interacts with Raf, a serine/threonine protein kinase that is structurally similar to MAPKKKs, and brings Raf to the membrane. Activated Raf can then phosphorylate a MAPKK (reviewed in reference 142). Ras in mammalian cells is also proposed to play a role in the Rho family-mediated reorganization of the actin cytoskeleton (reviewed in reference 123).
The ras1 gene of S. pombe, like its mammalian counterpart, appears to regulate two different pathways (Fig. 10): a MAPK cascade pathway and a cell polarity and morphogenesis pathway involving a Rho family protein, Cdc42 (26, 130). The cell polarity and morphogenesis pathway includes proteins that are key regulators of polarity establishment: Cdc42, Scd1 (the proposed GEF for SpCdc42; homologous to S. cerevisiae Cdc24), and Scd2 (an SH3 domain-containing protein homologous to S. cerevisiae Bem1). Two-hybrid system analysis showed that interactions occur among these proteins and that Scd1 interacts with Ras1 (26). These observations led to the proposal that Ras1 activates Scd1, which then activates Cdc42. Activated Cdc42, in turn, activates Shk1 (Fig. 11). The shk1 gene, a homolog of S. cerevisiae STE20, is essential for growth.shk1 spores germinate and arrest
as spherical cells, which is also the phenotype exhibited by
cdc42 and scd1 mutants (130).
Several arguments have been used to propose a role for Shk1 in the
pheromone response pathway (Fig. 10) (130), but resolution
of its participation in this pathway awaits more conclusive
experiments. Because the phenotype of ras1 null mutants is
weaker than that of scd1, cdc42, or
shk1, null mutants it can be proposed that other inputs
besides Ras1 can activate the morphogenesis pathway.
MAPK Cascade Signalling and Dimorphism
Pseudohyphal pathway of S. cerevisiae.
Pseudohyphal growth is a morphogenetic transition exhibited by
a/ cells under nitrogen starvation conditions
(62) and is widespread in nature (66, 207). This
transition entails changes in cell morphology, budding pattern, and
cell separationcells switch from an ovoid to an elongated shape; they
bud apically, and the buds remain attached, resulting in chains of
attached cells; and the cells acquire the ability to invade the agar
surface on which they are growing (62, 105). The switch to
this type of growth is thought to allow yeast cells to scavenge better
for nutrients; it has been observed that ovoid cells bud from the tips
of the pseudohyphae, effectively allowing new growth away from the
established colony (61). A similar but less exhuberant form
of pseudohyphal growth (invasive growth) is also exhibited by
a or cells in older colonies, where nutrients have presumably been depleted (174).
(i) MAPK cascade and transcriptional activators. Pseudohyphal growth is mediated in part by activation of a signalling pathway in response to nitrogen starvation. Remarkably, this signalling pathway involves many but not all of the components used in the pheromone response pathway: Ste20 (p65PAK), Ste11 (MAPKKK), Ste7 (MAPKK), and Ste12 (transcription factor) (121) (Fig. 12). The MAPK for this pathway could be Kss1 (125) (see below). Because Ste12 is the transcriptional activator for both the pheromone response and pseudohyphal growth pathways, a mechanism must exist for restricting the set of target genes activated. The interaction of Ste12 with another transcription factor, Tec1 (60, 126) (Fig. 12), appears to confer specificity of the response. Ste12-Tec1 recognizes a composite response element containing a Ste12 site and a Tec1 site, which is found in the TEC1 gene and in a gene activated by nutrient depletion (126). It is presumed that target genes for the pseudohyphal pathway have this composite site. The binding site for Tec1 is similar to that bound by the A. nidulans AbaA protein, a protein involved in a regulatory circuit controlling conidiophore development (4).
|
diploid cells, Kss1 may be responsible for inhibiting
Rst1 and Rst2 (39, 55). The observation that strains with
KSS1 deleted exhibit normal pseudohyphal growth would argue
against this role of Kss1. Recent results suggest that Kss1 plays a
dual role in pseudohyphal growth: a positive role, which is Ste7
dependent, and a negative role, which is Ste7 independent (see
reference 125 for details). Further analyses of Kss1
should help elucidate its role in this pathway.
(ii) Upstream of the MAPK cascade.
Neither the
receptors nor the heterotrimeric G protein for the pheromone response
pathway participates in signal sensing in the pseudohyphal pathway:
these genes are not expressed in a/ diploids. Ste5 is
also not needed for pseudohyphal growth (121). The signal
generated by nitrogen starvation appears to be mediated by Ras2 and
Cdc42, two small GTP binding proteins that act upstream of Ste20
(144) (Fig. 12), although it is not known if Ras2 is immediately upstream of Cdc42. The Cdc42 binding site in Ste20 has
recently been demonstrated to be necessary for pseudohyphal growth.
Since this site is necessary for interaction with Cdc42 in vitro and in
vivo, it appears that binding of Cdc42 to Ste20 activates Ste20 for its
function in pseudohyphal growth (109, 161). In addition to
these components, the two yeast homologs of 14-3-3 proteins, Bmh1 and
Bmh2, are implicated in the pseudohyphal pathway: they appear to
regulate transcriptional induction and cell elongation independently of
each other; their action may be exerted by interaction with the Ste20
protein (reference 173 and references therein).
(iii) Parallel pathways for pseudohyphal growth? Mutations in STE20 cause a more severe defect in pseudohyphal growth than do mutations in STE7 or in STE12; thus, Ste20 may regulate other targets in addition to the MAPK cascade (144, 173). Because deletion of STE7 and STE12 genes reduces but does not completely abolish pseudohyphal growth (121), it is likely that another pathway can promote pseudohyphal growth. The concerted action of both may be important for a full response. Parallel pathways for filamentous growth have also been proposed to exist in Candida albicans and U. maydis (see below).
The ELM genes may regulate an alternative pathway of pseudohyphal growth or some aspect of the pseudohyphal transition in S. cerevisiae. The normal function of these genes appears to be the inhibition of pseudohyphal growth under optimal growth conditions, although the specific function of most of these gene products is unknown (14, 15). ELM1 encodes a protein kinase whose absence leads to a constitutive pseudohyphal morphology: elongated cells that remain attached. Because the elongated morphology of pseudohyphal cells may reflect altered levels of Cdk activity (119) and because of genetic interactions of ELM1 with other genes that impinge on Cdk, it has been proposed that ELM1 functions in a pathway involving other protein kinases that regulate Cdk activity (51a, 144a). Other genes controlling pseudohyphal growth have also been identified and include PHD1 and SOK2 (61, 143, 216). Sok2 appears to antagonize pseudohyphal growth, whereas Phd1 appears to promote it: they may either act in a linear pathway or converge independently on the same target. Their relationship to Ste12 and Tec1 remains to be determined. Both Phd1 and Sok2 share amino acid similarity with transcriptional activators of cell cycle-regulated genes and to the StuA protein of Aspergillus nidulans (140). StuA controls a developmental program leading to conidiophore formation. A cascade of regulatory proteins similar to that governing conidiophore development in A. nidulans (reviewed in reference 139; see also reference 23) may govern pseudohyphal growth in yeast.Signalling and dimorphism in other fungi: C. albicans and U. maydis. Two fungi, C. albicans and U. maydis, have attracted renewed interest in fungal dimorphism because of its link to pathogenicity.
C. albicans, an imperfect fungus (i.e., no sexual stage), is an opportunistic pathogen of immunocompromised patients and has become a major pathogen in nosocomial infections. It has the ability to switch from a yeast-like to a pseudohyphal form and also to a true hyphal form. (Growth of a hypha is by apical extension, and division occurs in a fission-like manner, whereas pseudohyphae arise by budding.) The dimorphic transition in C. albicans is mediated in part by the same signalling components that regulate pseudohyphal growth in S. cerevisiae: Cst20 (a homolog of Ste20), Hst7 (a homolog of Ste7), and Cph1 (a homolog of Ste12) (102, 111, 120). Because these components are required under some conditions but are dispensable under others, it has been proposed that alternative pathways exist for activation of filamentous growth in C. albicans. The question of how the dimorphic switch and pathogenicity are coupled remains unclear. It is possible that switching to different forms allows this fungus to evade the host immune response. In contrast to C. albicans, in the basidiomycete fungus U. maydis a distinct relationship exists between form and pathogenicity: the haploid yeast form is nonpathogenic, whereas the dikaryotic filamentous form is pathogenic on maize (reviewed in references 6, 7, and 92). Dimorphism in this fungus is governed by two mating-type loci: a controls a pheromone signalling pathway, and b encodes homeodomain regulatory proteins. The integrated input of both loci is required for filamentous growth in culture (reviewed in references 6 and 92). Formation of the filamentous pathogenic dikaryon comes about by fusion of haploid cells carrying different alleles at both loci, for example, a1 b1 and a2 b2. Cell fusion is governed by the a locus with two alleles (a1 and a2), each of which contains genes that code for a pheromone precursor and a receptor (17). Thus, as in yeast, cell fusion is controlled by the interaction of pheromones with receptors. Surprisingly, in culture, different a alleles (that is, different pheromones and receptors) are required for hyphal growth, which indicates that an autocrine-like response (i.e., self-stimulation) governs filamentous growth (11, 195). This autocrine response requires, in addition to the pheromones and receptors, a G (Gpa3) protein, a
MAPKK (Fuz7), and a transcription factor (Prf1), all of which may be
components of a pheromone response pathway (9, 69, 170). The
requirement for pheromones and receptors contrasts with budding yeast,
where these elements are not necessary for pseudohyphal growth of
a/ diploids.
Dimorphism is also regulated by cAMP levels: high levels promote
yeast-like growth, whereas low levels promote filamentous growth
(63), a situation reminiscent of the regulation of sexual development by cAMP levels in S. pombe. Because nitrogen
starvation is required for filamentous growth (10), one
possibility is that, as in S. pombe, nitrogen starvation
lowers cAMP levels. In S. pombe, the G protein Gpa2
regulates cAMP levels in response to nutritional conditions
(90). Therefore, cAMP levels in U. maydis, in
principle, could be controlled by a G protein that senses
nutritional status.
Because different a alleles are not necessary for the
development of hyphae in planta, it has been proposed that plant
signals activate the pathway activated by pheromones or an alternative pathway for filamentous growth (8).
Mate as You Wish: What Matters Is What You Are after Mating
We have already seen that filamentous growth in U. maydis entails the input of pheromones and receptors and
homeodomain proteins. The pheromone and receptor system is simple in
that there are only two receptors (Pra1 and Pra2) and two pheromones
(Mfa1 and Mfa2). Pra1 is activated by Mfa2 and Pra2 by Mfa1
(17). In the world of the mushrooms (which, like U. maydis, are Basidiomycete fungi), life is not so simple: the life
cycle of Schizophyllum commune and Coprinus
cinereus is regulated by two mating complexes, A and
B, each containing two loci, and . The and loci are both multiallelic (for further details, see references
25a, 106, 196, 209, and 220).
These fungi exist only as filaments, which are of two types,
monokaryotic and dikaryotic; only the latter can produce a fruiting
body (the mushroom). Mating occurs between cells of homokaryotic
filaments and is not regulated (it's a free-for-all). Strikingly,
development of the dikaryotic filament after mating is exquisitely
regulated by the coordinate action of the A and B
mating complexes (reviewed in references 25a and
103).
Events regulated by the A and B
complexes.
To understand the possible role of pheromones and
receptors in the life cycle of these fungi, I first give a synopsis of
the events regulated by A and B (Fig.
13A). After mating, reciprocal exchange
of nuclei occurs (Fig. 13A, step 1); this is followed by migration of
the invading nucleus through the hypha until it reaches the tip cell
(step 2). Septa dissolve to allow passage of the migrating nucleus. In
the tip cell, the invading and resident nuclei pair and establish
dikaryosis (step 2). Division of this dikaryotic cell occurs through an
ornate process as follows: the tip cell forms an appendage (hook cell
or clamp connection) that curves towards the subapical cell, coordinate
division (conjugate division) occurs, and one nucleus migrates into the
appendage (step 3). Three cells are created: a dikaryotic tip cell, a
subapical cell with one nucleus, and an appendage with one nucleus
(step 4). The appendage fuses with the subapical cell and delivers the nucleus so that dikaryosis is established in this cell (step 5). The
fusion of this appendage to the subapical cell can be viewed as mating
between two yeast cells. Not surprisingly, this particular step is
regulated by the B complex, which encodes pheromone
precursors and receptors. This division process requires different
alleles at A or A and at B or
B (reviewed in references 25a, 103, and 210) (see the legend to Fig. 13 for the steps
regulated by A).
|
Multiple pheromones and receptors regulate a specialized
form of cell fusion.
To simplify the following discussion, I
consider only the B locus of Schizophyllum
commune. Two of nine different alleles have been cloned and
sequenced (209). The remarkable finding is that each
contains three genes encoding putative precursors for lipopeptides like
the a-factor of S. cerevisiae (Fig. 13B) and also
a gene encoding a Ste3-like putative seven transmembrane receptor (Fig.
13B). Although the structural organization of the receptors is
conserved, the amino acid sequences of R1 and R2 are not identical
(Fig. 13B). The putative pheromones within a given allele are different
from each other: 1-1 is different from 1-2 and 1-3 and from the
putative pheromones of the other allele (2-1, 2-2, and 2-3, and so on)
(Fig. 13B). The pheromones encoded by allele 1 do not activate R1, but
some can activate R2. Conversely, the pheromones encoded by allele 2 do
not activate R2, but some can activate R1. It appears that a given
pheromone, for example 1-1, can activate more than one receptor, for
example R2, R3, etc., and that a given receptor, for example R2, can be
activated by multiple pheromones, for example, 1-1, 1-2, and 1-3 (for
details, see references 209 and
220). Clearly, the pheromone system of the mushrooms
poses intriguing challenges.
Tales of G Proteins, Pheromones, and MAPK Components
In this section, I present information about various signalling components and their inferred roles in the life cycle of several filamentous fungi.
Heterotrimeric G proteins.
G subunits have been
identified in a number of fungi. I discuss only those in N. crassa, Cryphonectria parasitica, and U. maydis. A common theme emerging from these studies is that
multiple G subunits exist in a given fungus and may regulate diverse
aspects of the life cycle. The gna-1 gene of N. crassa, an Ascomycete fungus, encodes a Gi-type
protein that governs various aspects of the life cycle of this
organism: apical extension of hyphae, macroconidiation, female
fertility, and sensitivity to hyperosmolarity (91). Gna-1
might regulate these diverse processes via a common pathway, for
example by regulation of a MAPK cascade in response to different
stimuli, or perhaps Gna-1 regulates different signalling pathways.
subunits have been identified: CPG-1 and CPG-2. Infection of this
fungus by a virus results in attenuation of fungal virulence and
correlates with reduced levels of Cpg-1 protein and increased cAMP
levels. Drug-mediated elevation of cAMP levels mimics the attenuation
of virulence caused by viral infection, suggesting that Cpg-1, like
some mammalian counterparts, regulates adenylyl cyclase. Disruption of
CPG-1 indicates that Cpg-1 is required for optimal hyphal
growth, conidiation, female fertility, and virulence. Disruption of
CPG-2 had only marginal effects on the above processes
(30, 58). The processes regulated by Cpg-1 in C. parasitica are similar (except for virulence) to those regulated
by Gna-1 in N. crassa, which suggests that common pathways
in these fungi are regulated by these G subunits.
In U. maydis, four genes encoding G subunits,
gpa1 to gpa4, have been identified
(170). Gpa3 may be the pheromone receptor-coupled G protein.
Because pheromones and receptors are necessary for filamentous growth
(see the section on signalling and dimorphism in C. albicans
and U. maydis, above) and because Gpa3 appears to be
necessary for the pheromone-induced expression of pheromone genes, it
was not surprising that Gpa3 is also required for filamentous growth
(170). Activated alleles of gpa3 allow the mating
of strains carrying identical a alleles. Because wild-type
strains with identical a alleles do not mate, these results
suggest that the activated gpa3 allele leads to constitutive
activation of a putative pheromone response pathway, resulting in
mating. Gpa3 is similar to Gpa2 of S. pombe, which is
involved in nutrient sensing, and to CPG-2 of C. parasitica. It remains to be determined whether Gpa3 regulates cAMP levels or the pheromone MAPK cascade. The roles of
gpa1, gpa2, and gpa4 are unknown.
MAPKK, MAPK, and pheromones. The MAPKK Fuz7 of U. maydis is necessary for conjugation and filament formation in culture (see the section on signalling and dimorphism in C. albicans and U. maydis, above) (9). It is presumably involved in the pheromone response signalling pathway, although this remains to be conclusively demonstrated. In addition to this role, Fuz7 is necessary for pathogenicity: strains with fuz7 deleted are unable to induce tumors (9). This defect is not a consequence of an inability to produce filaments, since null mutants produce filaments in planta (8). It is thus hypothesized that Fuz7 is activated by a plant signal and that this activation is crucial for the fungus to induce tumors (9).
Pmk1 is a homolog of Fus3 and Kss1 in Magnaporthe grisea, an Ascomycete fungus that causes rice blast disease. This MAPK is required for formation of the appressorium, a specialized structure formed by many pathogenic fungi for invasion of plant cells. Deletion of PMK1 results in a defect in appressorium formation and thus in nonpathogenicity (225). The nature of the signal that activates this MAPK is not known. A remarkable finding about M. grisea is that S. cerevisiae-factor at high levels interferes with appressorium
formation and thus inhibits pathogenicity (see reference
12 for details). The effect was mating-type
specific, affecting cells of the MAT1-2 but not the MAT1-1 mating type.
Culture filtrates of MAT1-1 cells contain an activity that inhibits
appressorium formation of MAT1-2 cells, suggesting that pheromones and
a pheromone response pathway may regulate appressorium formation
(12). Pmk1 may be part of this pathway. Thus, it can be
speculated that this pathway plays two roles: in response to
pheromones, it activates mating and inhibits appressorium formation,
and in response to another signal, it inhibits mating and activates
appressorium formation.
CONCLUDING REMARKS
|
TopPreviousNextReferences
|
|---|
This tour of the different signalling pathways in the yeasts has
attempted to illustrate the use of the highly conserved MAPK cascade in
the transduction of diverse signals from the cell surface to the
interior of the cell. Despite the high conservation of this module and
the multiplicity of such modules within a single cell, the response to
a particular signal is very specific, with little cross talk between
pathways. The specificity of the response is due in part to
sequestering proteins that facilitate complex formation of the MAPK
cascade components and thus prevent inappropriate activation of other
pathways. Although this is an attractive mechanism for inhibition of
cross talk, only two examples of scaffold proteins have been
identifiedSte5 and Pbs2. This paucity may reflect our incomplete
knowledge of the other pathways or the existence of other mechanisms
that ensure specificity. One possibility, mentioned briefly in the
introductory comments to the MAPK cascade, is that the interaction of a
given MAPK with its activator and its substrates is very specific and
may be dictated by conformation of the proteins. The three-dimensional
structure of two mammalian MAPKs (ERK2 and p38) shows that they have
similar folding of several domains but different folding of other
domains. These differences may be critical for the specificity of
recognition and activation of a given MAPK by its MAPKK and for
substrate recognition and activation by the MAPK. As the
three-dimensional structures of other MAPKs, in both their inactive and
active states, become available, our understanding of the specificity
of MAPKs with their substrates and activators will be greatly
illuminated.
Although cross talk is generally not observed, it might be desirable under some conditions to coordinate the output of two responses. One example is the activation of the PKC pathway by pheromones during formation of mating projections. As our knowledge of these pathways deepens, we might also uncover other instances of communication between pathways.
Some other areas where our knowledge is sparse are the following. (i)
What is the mechanism by which a single pathway can be activated by
multiple signals, as is the case for the osmoresponse pathway in
S. pombe and the PKC pathway of S. cerevisiae?
This raises several questions, one of which concerns whether each
signal activates a specific sensor. If so, do targets activated in
response to different input signals differ? We have seen that
specificity may be conferred by different combinatorial activities of
transcriptional activators. (ii) What is the nature of the receptors
involved in the osmosensing pathways? These receptors may be
mechanosensors, of which we know very little. Thus, the identification
and characterization of these receptors is expected to shed
considerable light on our understanding of how these sensors become
activated and how they transduce the signal to downstream components.
(iii) How do components that reside in the membrane communicate with
the elements of the pathway that do not? This is likely to involve
adaptor proteins, one function of which might be the translocation of
cytoplasmic components to the membrane for activation. A specific
question is, for example, how does Ste5 become localized to the
membrane for interaction with G during activation of the
pheromone response pathway in S. cerevisiae? Translocation
might occur in a pheromone-dependent manner. (iv) How is the pheromone
response coupled with the machinery responsible for reorganization of
the actin cytoskeleton to cause morphological changes in response to
pheromone treatment?
The study of signalling pathways in filamentous fungi will predictably experience an explosion of information in the near future. Current information suggests that heterotrimeric G proteins control diverse aspects of their life cycle. In addition, MAPK cascade components appear to play crucial roles in pathogenicity. It is hoped that future studies will provide a better understanding of how different phases of the life cycle of filamentous fungi are regulated by signalling pathways.
ACKNOWLEDGMENTS
|
TopPreviousNextReferences
|
|---|
I thank Linda Huang for comments on the pheromone response section, Sean O'Rourke for comments on the S. cerevisiae osmolarity response section, Ira Herskowitz for valuable comments on the entire manuscript, Hiten Madhani for sharing unpublished results and for discussion, and anonymous reviewers for comments.
FOOTNOTES
* Mailing address: Department of Biochemistry and Biophysics, School of Medicine, University of California, 513 Parnassus Ave., Room S-960, San Francisco, CA 94143-0448. Phone: (415) 476-4985. Fax: (415) 476-0943. E-mail: banuett{at}cgl.ucsf.edu.
REFERENCES
|
TopPrevious |
|---|
| 1. | Aiba, H., H. Yamada, R. Ohmiya, and T. Mizuno. 1995. The osmoinducible gpd1+ gene is a target of the signaling pathway involving Wis1 MAP-kinase kinase in fission yeast. FEBS Lett. 376:199-201[Medline]. |
| 2. |
Albertyn, J.,
S. Hohmann,
J. M. Thevelein, and B. A. Prior.
1994.
GPD1, which encodes glycerol-3-phosphate dehydrogenase, is essential for growth under osmotic stress in Saccharomyces cerevisiae, and its expression is regulated by the high-osmolarity glycerol response pathway.
Mol. Cell. Biol.
14:4135-4144 |
| 3. |
Alex, L. A.,
K. A. Borkovich, and M. I. Simon.
1996.
Hyphal development in Neurospora crassa: involvement of a two-component histidine kinase.
Proc. Natl. Acad. Sci. USA
93:3416-3421 |
| 4. |
Andrianopoulos, A., and W. E. Timberlake.
1994.
The Aspergillus nidulans abaA gene encodes a transcriptional activator that acts as a genetic switch to control development.
Mol. Cell. Biol.
14:2503-2515 |
| 5. | Aono, T., H. Yanah, F. Miki, J. Davey, and C. Shimoda. 1994. Mating pheromone-induced expression of the mat1-Pm gene of Schizosaccharomyces pombe: identification of signalling components and characterization of upstream controlling elements. Yeast 10:757-770[Medline]. |
| 6. | Banuett, F. 1995. Genetics of Ustilago maydis, a fungal pathogen that induces tumors in maize. Annu. Rev. Genet. 29:179-208[Medline]. |
| 7. | Banuett, F. 1992. Ustilago maydis, the delightful blight. Trends Genet. 8:174-180[Medline]. |
| 8. | Banuett, F., and I. Herskowitz. 1996. Discrete developmental stages during teliospore formation in the corn smut fungus, Ustilago maydis. Development 122:2965-2976[Abstract]. |
| 9. |
Banuett, F., and I. Herskowitz.
1994.
Identification of Fuz7, a U. maydis MEK/MAPKK homologue required for a-dependent and independent processes in the fungal life cycle.
Genes Dev.
8:1367-1378 |
| 10. | Banuett, F., and I. Herskowitz. 1994. Morphological transitions in the life cycle of Ustilago maydis and their genetic control by the a and the b loci. Exp. Mycol. 18:247-266. |
| 11. |
Banuett, F., and I. Herskowitz.
1989.
Different a alleles of Ustilago maydis are necessary for maintenance of filamentous growth but not for meiosis.
Proc. Natl. Acad. Sci. USA
86:5878-5882 |
| 12. |
Beckerman, J. L.,
F. Nalder, and D. J. Ebbole.
1997.
Inhibition of pathogenicity of the rice blast fungus by Saccharomyces cerevisiae -factor.
Science
276:1116-1119 |
| 13. |
Berman, D. M.,
T. M. Wilkie, and A. G. Gilman.
1996.
GAIP and RGS4 are GTPase-activating proteins for the Gi subfamily of G protein subunits.
Cell
86:445-452[Medline].
|
| 14. | Blacketer, M. J., P. Madaule, and A. M. Myers. 1995. Mutational analysis of morphologic differentiation in Saccharomyces cerevisiae. Genetics 140:1259-1275[Abstract]. |
| 15. |
Blacketer, M. J.,
C. M. Koehler,
S. G. Coats,
A. M. Myers, and P. Madaule.
1993.
Regulation of dimorphism in Saccharomyces cerevisiae: involvement of the novel protein kinase homolog Elm1p and protein phosphatase 2A.
Mol. Cell. Biol.
13:5567-5581 |
| 16. |
Boguslawski, G.
1992.
PBS2, a yeast gene encoding a putative protein kinase, interacts with the RAS2 pathway and affects osmotic sensitivity of Saccharomyces cerevisiae.
J. Gen. Microbiol.
138:2425-2432 |
| 17. | Bölker, M., M. Urban, and R. Kahmann. 1992. The a mating type locus of U. maydis specifies cell signalling components. Cell 68:441-450[Medline]. |
| 18. |
Boone, C.,
N. G. Davis, and G. F. Sprague.
1993.
Mutations that alter the third cytoplasmic loop of the a-factor receptor lead to a constitutive and hypersensitive phenotype.
Proc. Natl. Acad. Sci. USA
90:9921-9925 |
| 19. | Bourne, H. R. 1997. How receptors talk to trimeric G proteins. Curr. Opin. Cell Biol. 9:134-142[Medline]. |
| 20. |
Brewster, J. L.,
T. de Valoir,
N. D. Dwyer,
E. Winter, and M. C. Gustin.
1993.
An osmosensing signal transduction pathway in yeast.
Science
259:1760-1763 |
| 21. |
Büküsoglu, G., and D. D. Jenness.
1996.
Agonist-specific conformational changes in the yeast -factor pheromone receptor.
Mol. Cell. Biol.
16:4818-4823[Abstract].
|
| 22. | Burbelo, P. D., D. Drechsel, and A. Hall. 1995. A conserved binding motif defines numerous candidate target proteins for both Cdc42 and Rac GTPases. J. Biol. Chem. 279:29071-29074. |
| 23. | Busby, T. M., K. Y. Miller, and B. L. Miller. 1996. Suppression and enhancement of the Aspergillus nidulans medusa mutation by altered dosage of the bristle and stunted genes. Genetics 143:155-163[Abstract]. |
| 24. | Cabib, E., T. Drgon, J. Drgonová, R. A. Ford, and R. Kollár. 1997. The yeast cell wall, a dynamic structure engaged in growth and morphology. Biochem. Soc. Trans. 25:200-204[Medline]. |
| 25. |
Cairns, B. R.,
S. W. Ramer, and R. D. Kornberg.
1992.
Order of action of components in the yeast pheromone response pathway revealed with a dominant allele of the Ste11 kinase and the multiple phosphorylation of the Ste7 kinase.
Genes Dev.
6:1305-1318 |
| 25a. |
Casselton, L. A., and N. S. Olesnicky.
1998.
Molecular genetics of mating recognition in basidiomycete fungi.
Microbiol. Mol. Biol. Rev.
62:55-70.
|
| 26. | Chang, E. C., M. Barr, Y. Wang, V. Jung, H.-P. Xu, and M. H. Wigler. 1994. Cooperative interaction of S. pombe proteins required for mating and morphogenesis. Cell 79:131-141[Medline]. |
| 27. | Chang, F. 1991. In Regulation of the cell cycle by a negative growth factor in yeast. Ph.D. thesis. University of California, San Francisco. |
| 28. | Chang, F., and P. Nurse. 1996. How fission yeast fission in the middle. Cell 84:191-194[Medline]. |
| 29. | Chang, F., and I. Herskowitz. 1990. Identification of a gene necessary for cell cycle arrest by a negative growth factor of yeast: FAR1 is an inhibitor of a G1 cyclin, Cln2. Cell 63:999-1011[Medline]. |
| 30. |
Chen, B.,
S. Gao,
G. H. Choi, and D. L. Nuss.
1996.
Extensive alteration of fungal gene transcript accumulation and elevation of G-protein-regulated cAMP levels by a virulence-attenuating hypovirus.
Proc. Natl. Acad. Sci. USA
93:7996-8000 |
| 31. |
Chen, Q., and J. B. Konopka.
1996.
Regulation of the -factor receptor by phosphorylation.
Mol. Cell. Biol.
16:247-257[Abstract].
|
| 32. | Choi, K.-Y., B. Satterberg, D. M. Lyons, and E. A. Elion. 1994. Ste5 tethers multiple protein kinases in the MAP kinase cascade required for mating in S. cerevisiae. Cell 78:499-512[Medline]. |
| 33. | Christensen, P. U., J. Davey, and O. Nielsen. 1997. The Schizosaccharomyces pombe mam1 gene encodes an ABC transporter mediating secretion of M-factor. Mol. Gen. Genet. 255:226-236[Medline]. |
| 34. |
Cid, V. J.,
A. Durán,
F. del Rey,
M. P. Snyder,
C. Nombela, and M. Sánchez.
1995.
Molecular basis of cell integrity and morphogenesis in Saccharomyces cerevisiae.
Microbiol. Rev.
59:345-386 |
| 35. | Clarke, S. 1992. Protein isoprenylation and methylation at carboxyl-terminal cysteine residues. Annu. Rev. Biochem. 61:355-386[Medline]. |
| 36. | Cohen, G. B., R. Ren, and D. Baltimore. 1995. Modular binding domains in signal transduction proteins. Cell 80:237-248[Medline]. |
| 37. |
Cook, J. G.,
L. Bardwell,
S. J. Kron, and J. Thorner.
1996.
Two novel targets of the MAP kinase Kss1 are negative regulators of invasive growth in the yeast Saccharomyces cerevisiae.
Genes Dev.
10:2831-2848 |
| 38. |
Costigan, C.,
S. Gherung, and M. Snyder.
1992.
A synthetic lethal screen identifies SLK1, a novel protein kinase homolog implicated in yeast cell morphogenesis and cell growth.
Mol. Cell. Biol.
12:1162-1178 |
| 39. | Courchesne, W. E., R. Kunisawa, and J. Thorner. 1989. A putative protein kinase overcomes pheromone-induced arrest of cell cycling in S. cerevisiae. Cell 58:1107-1119[Medline]. |
| 40. |
Davenport, K. R.,
M. Sohaskey,
Y. Kamada,
D. E. Levin, and M. C. Gustin.
1995.
A second osmosensing signal transduction pathway in yeast.
J. Biol. Chem.
270:30157-30161 |
| 41. | Davey, J. 1996. M-factor, a farnesylated mating factor from the fission yeast Schizosaccharomyces pombe. Biochem. Soc. Trans. 24:718-723[Medline]. |
| 42. | Davey, J. 1992. Mating pheromones of the fission yeast Schizosaccharomyces pombe: purification and structural characterization of M-factor and isolation and analysis of two genes encoding the pheromone. EMBO J. 11:951-960[Medline]. |
| 43. | Degols, G., K. Shiozaki, and P. Russell. 1996. Activation and regulation of the Spc1 stress-activated protein kinase in Schizosaccharomyces pombe. Mol. Cell. Biol. 16:2870-2877[Abstract]. |
| 44. |
Dekker, L. V., and P. J. Parker.
1994.
Protein kinase Ca question of specificity.
Trends Biochem. Sci.
19:73-77[Medline].
|
| 45. |
Dietzel, C., and J. Kurjan.
1987.
Pheromonal regulation and sequence of the Saccharomyces cerevisiae SST2 gene: a model for desensitization to pheromone.
Mol. Cell. Biol.
7:4169-4177 |
| 46. | Divecha, N., and R. F. Irvine. 1995. Phospholipid signalling. Cell 80:269-278[Medline]. |
| 47. | Dodou, E., and R. Treisman. 1997. The Saccharomyces cerevisiae MADS-box transcription factor Rlm1 is a target for the Mpk1 mitogen-activated protein kinase pathway. Mol. Cell. Biol. 17:1848-1859[Abstract]. |
| 48. |
Dohlman, H. G.,
J. Song,
D. Ma,
W. E. Courchesne, and J. Thorner.
1996.
Sst2, a negative regulator of pheromone signalling in the yeast Saccharomyces cerevisiae: expression, localization and genetic interaction and physical association with Gpa1 (the G-protein subunit).
Mol. Cell. Biol.
16:5194-5209[Abstract].
|
| 49. | Doi, K., A. Gartner, G. Ammerer, B. Errede, H. Shinkawa, K. Sugimoto, and K. Matsumoto. 1994. Msg5, a novel protein phosphatase promotes adaptation to pheromone response in S. cerevisiae. EMBO J. 13:61-70[Medline]. |
| 50. |
Douglas, C. M.,
F. Foor,
J. A. Marrinan,
N. Morin,
J. B. Nielsen,
A. M. Dahl,
P. Mazur,
W. Gainsky,
W. Li,
M. El-Sherbeini,
J. A. Clemas,
S. M. Mandal,
B. R. Frommer, and M. B. Kurtz.
1994.
The Saccharomyces cerevisiae FKS1 (ETG1) gene encodes an integral membrane protein which is a subunit of 1,3--D-glucan synthases.
Proc. Natl. Acad. Sci. USA
91:12907-12911 |
| 51. | Drgonová, J., T. Drgon, K. Tanaka, R. Kollár, G.-C. Chen, R. A. Ford, C. S. M. Chan, Y. Takai, and E. Cabib. 1996. Rho1p, a yeast protein at the interface between cell polarization and morphogenesis. Science 272:277-279[Abstract]. |
| 51a. | Edgington, N., and A. Myers. 1996. Suppressor analysis of the kinase Elm1 identifies a dominant allele of a S. pombe nim1+ homologue in S. cerevisiae, p. 108. In Abstracts of the Yeast Genetics and Molecular Biology Meeting. |
| 52. | Egger, L. A., H. Park, and M. Inouye. 1997. Signal transduction via the histidyl-aspartyl phosphorelay. Genes Cells 2:167-184. [Abstract] |
| 53. | Elion, E. A. 1995. Ste5: a meeting place for MAP kinases and their associates. Trends Cell Biol. 5:322-327. [Medline] |
| 54. | Elion, E. A., B. Satterberg, and J. E. Kranz. 1993. Fus3 phosphorylates multiple components of the mating signal transduction cascade: evidence for Ste12 and Far1. Mol. Biol. Cell 4:495-510[Abstract]. |
| 55. | Elion, E. A., P. L. Grisafi, and G. R. Fink. 1990. FUS3 encodes a Cdc2/Cdc28-related kinase required for the transition from mitosis into conjugation. Cell 60:649-664[Medline]. |
| 56. | Errede, B., A. Gartner, Z. Zhou, K. Nasmyth, and G. Ammerer. 1993. MAP kinase-related Fus3 from S. cerevisiae is activated by Ste7 in vitro. Nature 362:261-264[Medline]. |
| 57. |
Galcheva-Gargova, Z.,
B. Dérijard,
I.-H. Wu, and R. J. Davis.
1994.
An osmosensing signal transduction pathway in mammalian cells.
Science
265:806-808 |
| 58. |
Gao, S., and D. L. Nuss.
1996.
Distinct roles for two G protein subunits in fungal virulence, morphology, and reproduction revealed by targeted disruption.
Proc. Natl. Acad. Sci. USA
93:14122-14227 |
| 59. |
Gartner, A.,
K. Nasmyth, and G. Ammerer.
1992.
Signal transduction in Saccharomyces cerevisiae requires tyrosine and threonine phosphorylation of Fus3 and Kss1.
Genes Dev.
6:1280-1292 |
| 60. | Gavrias, V., A. Andrianopoulos, C. J. Gimeno, and W. E. Timberlake. 1996. Saccharomyces cerevisiae TEC1 is required for pseudohyphal growth. Mol. Microbiol. 19:1255-1263[Medline]. |
| 61. |
Gimeno, C. J., and G. R. Fink.
1994.
Induction of pseudohyphal growth by overexpression of PHD1, a Saccharomyces cerevisiae gene related to transcriptional regulators of fungal development.
Mol. Cell. Biol.
14:2100-2112 |
| 62. | Gimeno, C. J., P. O. Ljungdahl, C. A. Styles, and G. R. Fink. 1992. Unipolar cell divisions in the yeast S. cerevisiae lead to filamentous growth: regulation by starvation and RAS. Cell 68:1077-1090[Medline]. |
| 63. |
Gold, S.,
G. Duncan,
K. Barrett, and J. W. Kronstad.
1994.
cAMP regulates morphogenesis in the fungal pathogen Ustilago maydis.
Genes Dev.
8:2805-2816 |
| 64. |
Gotoh, Y.,
E. Nishida,
M. Shimanuki,
T. Toda,
Y. Imai, and M. Yamamoto.
1993.
Schizosaccharomyces pombe Spk1 is a tyrosine-phosphorylated protein functionally related to Xenopus mitogen-activated protein kinase.
Mol. Cell. Biol.
13:6427-6434 |
| 65. | Gray, J. V., J. P. Ogas, Y. Kamada, M. Stone, D. E. Levin, and I. Herskowitz. 1997. A role for the Pkc1-MAP kinase pathway of Saccharomyces cerevisiae in bud emergence and identification of a putative upstream regulator. EMBO J. 16:4924-4937[Medline]. |
| 66. | Guillermond, A. 1920. In The yeasts. John Wiley & Sons, New York, N.Y. |
| 67. |
Han, J.,
J.-D. Lee,
L. Bibbs, and R. J. Ulevitch.
1994.
A MAP kinase targeted by endotoxin and hyperosmolarity in mammalian cells.
Science
265:808-811 |
| 68. | Hanks, S. K., and T. Hunter. 1995. The eukaryotic protein kinase superfamily: kinase (catalytic) domain structure and classification. FASEB J. 9:576-596[Abstract]. |
| 69. | Hartmann, H. A., R. Kahmann, and M. Bölker. 1996. The pheromone response factor coordinates filamentous growth and pathogenicity in Ustilago maydis. EMBO J. 15:1632-1641[Medline]. |
| 70. |
Hartwell, L. H.
1980.
Mutants of Saccharomyces cerevisiae unresponsive to cell division control by polypeptide mating hormone.
J. Cell Biol.
85:811-822 |
| 71. |
Hasson, M. S.,
D. Blinder,
J. Thorner, and D. D. Jenness.
1994.
Mutational activation of the STE5 gene product bypasses the requirement for G protein and subunits in the yeast pheromone response pathway.
Mol. Cell. Biol.
14:1054-1065 |
| 72. | Hayles, J., and P. Nurse. 1992. Genetics of the fission yeast Schizosaccharomyces pombe. Annu. Rev. Genet. 26:373-402[Medline]. |
| 73. | Herskowitz, I. 1995. MAPK kinase pathways in yeast: for mating and more. Cell 80:187-197[Medline]. |
| 74. |
Herskowitz, I.
1988.
Life cycle of the budding yeast Saccharomyces cerevisiae.
Microbiol. Rev.
52:536-553 |
| 75. | Hicke, L., and H. Riezman. 1996. Ubiquitination of a yeast plasma membrane receptor signals its ligand-stimulated endocytosis. Cell 84:277-287[Medline]. |
| 76. | Hill, C. S., and R. Treisman. 1995. Transcriptional regulation by extracellular signals: mechanisms and specificity. Cell 80:199-211[Medline]. |
| 77. | Hirayama, T., T. Maeda, H. Saito, and K. Shinozaki. 1995. Cloning and characterization of seven cDNAs for hyperosmolarity-responsive (HOR) genes of Saccharomyces cerevisiae. Mol. Gen. Genet. 249:127-138[Medline]. |
| 78. |
Hirschman, J. E.,
G. S. De Zutter,
W. F. Simonds, and D. D. Jenness.
1997.
The G complex of the yeast pheromone response pathway.
J. Biol. Chem.
272:240-248 |
| 79. | Hughes, D. A. 1995. Control of signal transduction and morphogenesis by Ras. Semin. Cell Biol. 6:89-94[Medline]. |
| 80. | Hughes, D. A., N. Yabana, and M. Yamamoto. 1994. Transcriptional regulation of a Ras nucleotide-exchange factor gene by extracellular signals in fission yeast. J. Cell Sci. 107:3635-3642[Abstract]. |
| 81. | Hung, W., K. A. Olson, A. Breitkreutz, and I. Sadowski. 1997. Characterization of the basal and pheromone-stimulated phosphorylation states of Ste12p. Eur. J. Biochem. 245:241-251[Medline]. |
| 82. | Hunter, T. 1995. Protein kinases and phosphatases: the yin and yang of protein phosphorylation and signaling. Cell 80:225-236[Medline]. |
| 83. | Hunter, T., and G. D. Plowman. 1997. The protein kinases of budding yeast: six score and more. Trends Biochem. Sci. 22:18-22[Medline]. |
| 84. | Igual, J. C., A. L. Johnson, and L. H. Johnston. 1996. Coordinated regulation of gene expression by the cell cycle transcription factor Swi4 and the protein kinase C MAP kinase pathway for yeast cell integrity. EMBO J. 15:5001-5013[Medline]. |
| 85. |
Imai, Y., and M. Yamamoto.
1994.
The fission yeast mating pheromone P-factor: its molecular structure, gene structure, and ability to induce gene expression and G1 arrest in the mating partner.
Genes Dev.
8:328-338 |
| 86. |
Imai, Y., and M. Yamamoto.
1992.
Schizosaccharomyces pombe sxa1+ and sxa2+ encode putative proteases involved in the mating response.
Mol. Cell. Biol.
12:1827-1834 |
| 87. |
Inoue, S. B.,
H. Qadota,
M. Arisawa,
Y. Anraku,
T. Watanabe, and Y. Ohya.
1996.
Signalling toward yeast 1,3--glucan synthesis.
Cell Struct. Funct.
21:395-402[Medline].
|
| 88. |
Irie, K.,
M. Takase,
K. S. Lee,
D. E. Levin,
H. Araki,
K. Matsumoto, and Y. Oshima.
1993.
MKK1 and MKK2, which encode Saccharomyces cerevisiae mitogen-activated protein kinase-kinase homologs, function in the pathway mediated by protein kinase C.
Mol. Cell. Biol.
13:3076-3083 |
| 89. | Irie, K., H. Araki, and Y. Oshima. 1991. A new protein kinase, Ssp31, modulating the SMP3 gene product involved in plasmid maintenance in Saccharomyces cerevisiae. Gene 108:139-144[Medline]. |
| 90. |
Isshiki, T.,
N. Mochizuki,
T. Maeda, and M. Yamamoto.
1992.
Characterization of a fission yeast gene, gpa2, that encodes a G subunit involved in the monitoring of nutrition.
Genes Dev.
6:2455-2462 |
| 91. |
Ivey, F. D.,
P. N. Hodge,
G. E. Turner, and K. A. Borkovich.
1996.
The Gi homologue gna-1 controls multiple differentiation pathways in Neurospora crassa.
Mol. Biol. Cell
7:1283-1297[Abstract].
|
| 92. | Kahmann, R., T. Romeis, M. Bölker, and J. Kämper. 1995. Control of mating and development in Ustilago maydis. Curr. Opin. Genet. Dev. 5:559-564[Medline]. |
| 93. |
Kallal, L., and J. Kurjan.
1997.
Analysis of the receptor binding domain of Gpa1p, the G subunit involved in the yeast pheromone response pathway.
Mol. Cell. Biol.
17:2897-2907[Abstract].
|
| 94. |
Kamada, Y.,
H. Qadota,
C. P. Python,
Y. Anraku,
Y. Ohya, and D. E. Levin.
1996.
Activation of yeast protein kinase C by Rho1 GTPase.
J. Biol. Chem.
271:9193-9196 |
| 95. |
Kamada, Y.,
U. S. Jung,
J. Piotrowski, and D. E. Levin.
1995.
The protein kinase C-activated MAP kinase pathway of Saccharomyces cerevisiae mediates a novel aspect of the heat shock response.
Genes Dev.
9:1559-1571 |
| 96. | Kanoh, J., Y. Watanabe, M. Ohsugi, Y. Iino, and M. Yamamoto. 1996. Schizosaccharomyces pombe gad7+ encodes a phosphoprotein with a bZIP domain, which is required for proper G1 arrest and gene expression under nitrogen starvation. Genes Cells 1:391-408. [Abstract] |
| 97. | Kato, T., K. Okazaki, H. Murakami, S. Stettler, P. A. Fantes, and H. Okayama. 1996. Stress signal, mediated by a Hog1-like MAP kinase, controls sexual development in fission yeast. FEBS Lett. 378:207-212[Medline]. |
| 98. | Kitamura, K., and C. Shimoda. 1991. The Schizosaccharomyces pombe mam2 gene encodes a putative pheromone receptor which has a significant homology with the Saccharomyces cerevisiae Ste2 protein. EMBO J. 10:3743-3751[Medline]. |
| 99. | Kjærulff, S., D. Dooijes, H. Clevers, and O. Nielsen. 1997. Cell differentiation by interaction of two HMG-box proteins: Mat1-Mc activates M cell-specific genes in S. pombe by recruiting the ubiquitous transcription factor Ste11 to weak binding sites. EMBO J. 16:4021-4033[Medline]. |
| 100. |
Kjærulff, S.,
J. Davey, and O. Nielsen.
1994.
Analysis of the structural genes encoding M-factor in the fission yeast Schizosaccharomyces pombe: identification of a third gene, mfm3.
Mol. Cell. Biol.
14:3895-3905 |
| 101. |
Koelle, M. R.
1997.
A new family of G-protein regulatorsthe RGS proteins.
Curr. Opin. Cell Biol.
9:143-147[Medline].
|
| 102. |
Köhler, J. R., and G. R. Fink.
1996.
Candida albicans strains heterozygous and homozygous for mutations in mitogen-activated protein kinase signaling components have defects in hyphal development.
Proc. Natl. Acad. Sci. USA
93:13223-13228 |
| 103. | Kothe, E. 1996. Tetrapolar fungal mating types: sexes by the thousands. FEMS Microbiol. Rev. 18:65-87[Medline]. |
| 104. |
Kranz, J. E.,
B. Satterberg, and E. A. Elion.
1994.
The MAP kinase Fus3 associates with and phosphorylates the upstream signaling component Ste5.
Genes Dev.
8:313-327 |
| 105. | Kron, S. J., C. A. Styles, and G. R. Fink. 1994. Symmetric cell division in pseudohyphae of the yeast Saccharomyces cerevisiae. Mol. Biol. Cell 5:1003-1022[Abstract]. |
| 106. | Kües, U., R. N. Asante-Owusu, E. S. Mutasa, A. M. Tymon, E. H. Pardo, S. F. O'Shea, B. Göttgens, and L. A. Casselton. 1994. Two classes of homeodomain proteins specify the multiple A mating types of the mushroom Coprinus cinereus. Plant Cell 6:1467-1475[Abstract]. |
| 107. | Kurjan, J. 1993. The pheromone response pathway in Saccharomyces cerevisiae. Annu. Rev. Genet. 27:147-179[Medline]. |
| 108. | Kyriakis, J. M., P. Banerjee, E. Nikolakakl, T. Dai, E. A. Rubie, M. F. Ahmad, J. Avruch, and J. R. Woodgett. 1994. The stress-activated protein kinase subfamily of c-Jun kinases. Nature 369:156-160[Medline]. |
| 109. | Leberer, E., C. Wu, T. Leeuw, A. Fourest-Lieuvin, J. W. Segall, and D. Y. Thomas. 1997. Functional characterization of the Cdc42p binding domain of yeast Ste20p protein kinase. EMBO J. 16:83-97[Medline]. |
| 110. | Leberer, E., D. Y. Thomas, and M. Whiteway. 1997. Pheromone signalling and polarized morphogenesis in yeast. Curr. Opin. Genet. Dev. 7:59-66[Medline]. |
| 111. |
Leberer, E.,
D. Harcus,
I. D. Broadbent,
K. L. Clark,
D. Dignard,
K. Ziegelbauer,
A. Schmidt,
N. A. R. Gow,
A. J. P. Brown, and D. Y. Thomas.
1996.
Signal transduction through homologs of the Ste20p and Ste7p protein kinases can trigger hyphal formation in the pathogenic fungus Candida albicans.
Proc. Natl. Acad. Sci. USA
93:13217-13222 |
| 112. | Leberer, E., D. Dignard, D. Harcus, L. Hoogan, M. Whiteway, and D. Y. Thomas. 1993. Cloning of Saccharomyces cerevisiae STE5 as a suppressor of a Ste20 protein kinase mutant: structural and functional similarity of Ste5 to Far1. Mol. Gen. Genet. 241:241-254[Medline]. |
| 113. |
Leberer, E.,
D. Dignard,
D. Harcus,
D. Y. Thomas, and M. Whiteway.
1992.
The protein kinase homologue Ste20p is required to link the yeast pheromone response G-protein subunits to downstream signalling components.
EMBO J.
11:4815-4824[Medline].
|
| 114. |
Lee, K. S.,
K. Irie,
Y. Gotoh,
Y. Watanabe,
H. Araki,
E. Nishida,
K. Matsumoto, and D. E. Levin.
1993.
A yeast mitogen-activated protein kinase homolog (Mpk1p) mediates signalling by protein kinase C.
Mol. Cell. Biol.
13:3067-3075 |
| 115. |
Lee, K. S., and D. E. Levin.
1992.
Dominant mutations in a gene encoding a putative protein kinase (BCK1) bypass the requirement for a Saccharomyces cerevisiae protein kinase C homolog.
Mol. Cell. Biol.
12:172-182 |
| 116. |
Leeuw, T.,
A. Fourest-Lieuvin,
C. Wu,
J. Chenevert,
K. Clark,
M. Whiteway,
D. Y. Thomas, and E. Leberer.
1995.
Pheromone response in yeast: association of Bem1p with proteins of the MAP kinase cascade and actin.
Science
270:1210-1213 |
| 117. |
Levin, D. E., and E. Bartlett-Heubusch.
1992.
Mutants in the S. cerevisiae PKC1 gene display a cell cycle-specific osmotic stability defect.
J. Cell Biol.
116:1221-1229 |
| 118. | Levin, D. E., F. O. Fields, R. Kunisawa, J. M. Bishop, and J. Thorner. 1990. A candidate protein kinase C gene, PKC1, is required for the S. cerevisiae cell cycle. Cell 62:213-224[Medline]. |
| 119. | Lew, D. J., and S. I. Reed. 1995. Cell cycle control of morphogenesis in budding yeast. Curr. Opin. Genet. Dev. 5:17-23[Medline]. |
| 120. |
Liu, H.,
J. Köhler, and G. R. Fink.
1994.
Suppression of hyphal formation in Candida albicans by mutation of a STE12 homolog.
Science
266:1723-1726 |
| 121. |
Liu, H.,
C. A. Styles, and G. R. Fink.
1993.
Elements of the yeast pheromone response pathway required for filamentous growth of diploids.
Science
262:1741-1744 |
| 122. | Ma, D., J. G. Cook, and J. Thorner. 1995. Phosphorylation and localization of Kss1, a MAP kinase of the Saccharomyces cerevisiae pheromone response pathway. Mol. Biol. Cell 6:889-909[Abstract]. |
| 123. |
Machesky, L. M., and A. Hall.
1996.
Rhoa connection between membrane receptor signalling and the cytoskeleton.
Trends Cell Biol.
6:304-310.
[Medline] |
| 124. |
MacKay, V. L., and T. R. Manney.
1974.
Mutations affecting sexual conjugation and related processes in Saccharomyces cerevisiae. I. Isolation and phenotypic characterization of nonmating mutants.
Genetics
76:255-271 |
| 125. | Madhani, H. D., C. A. Styles, and G. R. Fink. 1997. MAP kinases with distinct inhibitory functions impart signaling specificity during yeast differentiation. Cell 91:673-684[Medline]. |
| 126. |
Madhani, H. D., and G. R. Fink.
1997.
Combinatorial control required for the specificity of yeast MAPK signaling.
Science
275:1314-1317 |
| 127. |
Maeda, T.,
M. Takekawa, and H. Saito.
1995.
Activation of yeast PBS2 MAPKK by MAPKKKs or by binding of an SH3-containing osmosensor.
Science
269:554-558 |
| 128. | Maeda, T., S. M. Wurgler-Murphy, and H. Saito. 1994. A two-component system that regulates an osmosensing MAP kinase cascade in yeast. Nature 239:242-245. |
| 129. | Marchler, G., C. Schüller, G. Adam, and H. Ruis. 1993. A Saccharomyces cerevisiae UAS element controlled by protein kinase A activates transcription in response to a variety of stress conditions. EMBO J. 12:1997-2003[Medline]. |
| 130. |
Marcus, S.,
A. Polverino,
E. Chang,
D. Robbins,
M. H. Cobb, and M. H. Wigler.
1995.
Shk1, a homolog of the Saccharomyces cerevisiae Ste20 and mammalian p65PAK protein kinases, is a component of a Ras/Cdc42 signalling module in the fission yeast Schizosaccharomyces pombe.
Proc. Natl. Acad. Sci. USA
92:6180-6184 |
| 131. |
Marcus, S.,
A. Polverino,
M. Barr, and M. Wigler.
1994.
Complexes between Ste5 and components of the pheromone-responsive mitogen-activated protein kinase cascade module.
Proc. Natl. Acad. Sci. USA
91:7762-7766 |
| 132. | Marsh, L., A. M. Neiman, and I. Herskowitz. 1991. Signal transduction during pheromone response in yeast. Annu. Rev. Cell Biol. 7:699-728. |
| 133. | Marshall, C. J. 1995. Specificity of receptor tyrosine kinase signaling: transient versus sustained extracellular signal-regulated kinase activation. Cell 80:179-186[Medline]. |
| 134. |
Masuda, T.,
K. Kariya,
M. Shinkai,
T. Okada, and T. Kataoka.
1995.
Protein kinase Byr2 is a target of Ras1 in the fission yeast Schizosaccharomyces pombe.
J. Biol. Chem.
270:1979-1982 |
| 135. |
Mazur, P.,
N. Morin,
W. Baginsky,
M. El-Serbeini,
J. A. Clemas,
J. B. Nielsen, and F. Foor.
1995.
Differential expression and function of two homologous subunits of yeast 1,3--D-glucan synthase.
Mol. Cell. Biol.
15:5671-5681[Abstract].
|
| 136. |
Mazzoni, C.,
P. Zarzov,
A. Rambourg, and C. Mann.
1993.
The SLT2 (MPK1) MAP kinase homolog is involved in polarized cell growth in Saccharomyces cerevisiae.
J. Cell Biol.
123:1821-1833 |
| 137. | McLeod, M., M. Stein, and D. Beach. 1987. The product of the mei3+ gene, expressed under control of the mating-type locus, induces meiosis and sporulation in fission yeast. EMBO J. 6:729-736[Medline]. |
| 138. |
Millar, J. B. A.,
V. Buck, and M. G. Wilkinson.
1995.
Pyp1 and Pyp2 PTPases dephosphorylate an osmosensing MAP kinase controlling cell size at division in fission yeast.
Genes Dev.
9:2117-2130 |
| 139. | Miller, B. L. 1993. Brushing up on bristles: complex genes and morphogenesis in molds. Trends Genet. 9:293-295[Medline]. |
| 140. |
Miller, K. Y.,
J. Wu, and B. L. Miller.
1992.
StuA is required for cell pattern formation in Aspergillus.
Genes Dev.
6:1770-1782 |
| 141. |
Mol, P. C.,
H. M. Parks,
J. T. Mullins, and E. Cabib.
1994.
A GTP-binding protein regulates the activity of (1-3)--glucan synthase, an enzyme directly involved in cell wall morphogenesis.
J. Biol. Chem.
269:31267-31274 |
| 142. | Morrison, D. K., and R. E. Cutler. 1997. The complexity of Raf1 regulation. Curr. Opin. Cell Biol. 9:174-179[Medline]. |
| 143. | Mösch, H.-U., and G. R. Fink. 1997. Dissection of filamentous growth by transposon mutagenesis. Genetics 145:671-684[Abstract]. |
| 144. |
Mösch, H.-U.,
R. L. Roberts, and G. R. Fink.
1996.
Ras2 signals via the Cdc42/Ste20/mitogen-activated protein kinase module to induce filamentous growth in Saccharomyces cerevisiae.
Proc. Natl. Acad. Sci. USA
93:5352-5356 |
| 144a. | Myers, A. M., M. Blacketer, T. Bierwagen, and N. Edgington. 1996. Cyclin-dependent kinase (CDK) activity regulates multiple aspects of pseudohyphal growth, abstr., p. 4. In Abstracts of the Yeast Genetics and Molecular Biology Meeting. |
| 145. |
Nadin-Davis, S. A., and A. Nasim.
1990.
Schizosaccharomyces pombe ras1 and byr1 are functionally related genes of the ste family that affect starvation-induced transcription of mating-type genes.
Mol. Cell. Biol.
10:549-560 |
| 146. | Neel, B. G., and N. K. Tonks. 1997. Protein tyrosine phosphatases in signal transduction. Curr. Opin. Cell Biol. 9:193-204[Medline]. |
| 147. | Neer, E. J. 1995. Heterotrimeric G proteins: organizers of transmembrane signals. Cell 80:249-257[Medline]. |
| 148. |
Neiman, A. M., and I. Herskowitz.
1994.
Reconstitution of a yeast protein kinase cascade in vitro: activation of the yeast MEK homologue Ste7 by Ste11.
Proc. Natl. Acad. Sci. USA
91:3398-3402 |
| 149. | Neiman, A. M., B. J. Stevenson, H-P. Xu, G. F. Sprague, I. Herskowitz, M. Wigler, and S. Marcus. 1993. Functional homology of protein kinases required for sexual differentiation in Schizosaccharomyces pombe and Saccharomyces cerevisiae suggests a conserved signal transduction module in eukaryotic organisms. Mol. Biol. Cell 4:107-120[Abstract]. |
| 150. | Newton, A. C. 1997. Regulation of protein kinase C. Curr. Opin. Cell Biol. 9:161-167[Medline]. |
| 151. | Nielsen, O., T. Friis, and S. Kjærulff. 1996. The Schizosaccharomyces pombe map1 encodes an SRF/MCM1-related protein required for P-cell specific gene expression. Mol. Gen. Genet. 253:387-392[Medline]. |
| 152. | Nonaka, H., K. Tanaka, H. Hirano, T. Fujiwara, H. Kohno, M. Umikawa, A. Mino, and Y. Takai. 1995. A downstream target of RHO1 small GTP-binding protein is PKC1, a homolog of protein kinase C, which leads to activation of the MAP kinase cascade in Saccharomyces cerevisiae. EMBO J. 14:5931-5938[Medline]. |
| 153. | Nurse, P. 1997. The Josef Steiner Lecture. CDKs and cell-cycle control in fission yeast: relevance to other eukaryotes and cancer. Int. J. Cancer 71:707-708[Medline]. |
| 154. |
Obara, T.,
M. Nakafuku,
M. Yamamoto, and Y. Kaziro.
1991.
Isolation and characterization of a gene encoding a G-protein subunit from Schizosaccharomyces pombe: involvement in mating and sporulation pathways.
Proc. Natl. Acad. Sci. USA
88:5877-5881 |
| 155. | Ogas, J. 1992. In Identification and analysis of regulators of G1 progression in Saccharomyces cerevisiae. Ph.D. thesis. University of California, San Francisco. |
| 156. | Ohmiya, R., H. Yamada, K. Nakashima, H. Aiba, and T. Mizuno. 1995. Osmoregulation of fission yeast: cloning of two distinct genes encoding glycerol-3-phosphate dehydrogenase, one of which is reponsible for osmotolerance for growth. Mol. Microbiol. 18:963-973[Medline]. |
| 156a. | O'Rourke, S. Personal communication. |
| 157. | Ozaki, K., K. Tanaka, H. Imamura, T. Hihara, T. Kameyama, H. Nonaka, H. Hirano, Y. Matsuura, and Y. Takai. 1996. Rom1p and Rom2p are GDP/GTP exchange proteins for the Rho1p small GTP binding protein in Saccharomyces cerevisiae. EMBO J. 15:2196-2207[Medline]. |
| 158. |
Paravicini, G.,
M. Cooper,
L. Friedli,
D. J. Smith,
J.-L. Carpentier,
L. S. Klig, and M. A. Payton.
1992.
The osmotic integrity of the yeast cell requires a functional PKC1 gene product.
Mol. Cell. Biol.
12:4896-4905 |
| 159. |
Park, H.-O.,
E. Bi,
J. R. Pringle, and I. Herskowitz.
1997.
Two active states of the Ras-related Bud1/Rsr1 protein bind to different effectors to determine yeast cell polarity.
Proc. Natl. Acad. Sci. USA
94:4463-4468 |
| 160. | Pelech, S. L. 1996. Signalling pathways: kinase connections on the cellular intranet. Curr. Biol. 6:551-554[Medline]. |
| 161. | Peter, M., A. M. Neiman, H.-O. Park, M. van Lohuizen, and I. Herskowitz. 1996. Functional analysis of the interaction between the small GTP binding protein Cdc42 and the Ste20 protein kinase in yeast. EMBO J. 15:7046-7059[Medline]. |
| 162. | Peter, M., A. Gartner, J. Horecka, G. Ammerer, and I. Herskowitz. 1993. FAR1 links the signal transduction pathway to the cell cycle machinery in yeast. Cell 73:747-760[Medline]. |
| 163. | Petersen, J., D. Weilguny, R. Egel, and O. Nielsen. 1995. Characterization of fus1 of Schizosaccharomyces pombe: a developmentally controlled function needed for conjugation. Mol. Cell. Biol. 15:3697-3707[Abstract]. |
| 164. |
Philips, J., and I. Herskowitz.
1997.
An osmosensing signal regulates cell fusion during mating in Saccharomyces cerevisiae.
J. Cell Biol.
138:961-974 |
| 165. |
Posas, F., and H. Saito.
1997.
Osmotic activation of the HOG MAPK pathway via Ste11p MAPKKK: scaffold role of Pbs2p MAPKK.
Science
276:1702-1705 |
| 166. | Posas, F., S. M. Wurgler-Murphy, T. Maeda, E. A. Witten, T. C. Thai, and H. Saito. 1996. Yeast HOG1 MAP kinase cascade is regulated by a multistep phosphorelay mechanism in the SLN1-YPD1-SSK1 "two-component" osmosensor. Cell 86:885-875. |
| 167. | Printen, J. A., and G. F. Sprague. 1994. Protein-protein interactions in the yeast pheromone response pathway: Ste5p interacts with all members of the MAP kinase cascade. Genetics 138:609-619[Abstract]. |
| 168. |
Qadota, H.,
C. P. Python,
S. B. Inoue,
M. Arisawa,
Y. Anraku,
Y. Zheng,
T. Watanabe,
D. E. Levin, and Y. Ohya.
1996.
Identification of yeast Rhop1p GTPase as a regulatory subunit of 1,3--glucan synthase.
Science
272:278-281.
|
| 169. |
Ramer, S. W., and R. W. Davis.
1993.
A dominant truncation allele identifies a gene, STE20, that encodes a putative protein kinase necessary for mating in Saccharomyces cerevisiae.
Proc. Natl. Acad. Sci. USA
90:452-456 |
| 170. | Regenfelder, E., T. Spellig, A. Hartmann, S. Lauenstein, M. Bölker, and R. Kahmann. 1997. G proteins in Ustilago maydis: transmission of multiple signals. EMBO J. 16:1934-1942[Medline]. |
| 171. | Rens-Domiano, S., and H. E. Hamm. 1995. Structural and functional relationships of heterotrimeric G-proteins. FASEB J. 9:1059-1066[Abstract]. |
| 172. |
Ridley, A. J.
1996.
Rhotheme and variations.
Curr. Biol.
6:1256-1264[Medline].
|
| 173. | Roberts, R. L., H.-U. Mösch, and G. R. Fink. 1997. 14-3-3 proteins bind Ste20p and are essential for Ras/MAPK cascade signaling in S. cerevisiae. Cell 89:1055-1065[Medline]. |
| 174. |
Roberts, R. L., and G. R. Fink.
1994.
Elements of a single MAP kinase cascade in Saccharomyces cerevisiae mediate two developmental programs in the same cell type: mating and invasive growth.
Genes Dev.
8:2974-2985 |
| 175. | Robinson, M. J., and M. H. Cobb. 1997. Mitogen-activated protein kinase pathways. Curr. Opin. Cell Biol. 9:180-186[Medline]. |
| 176. |
Roemer, T.,
G. Paravicini,
M. A. Payton, and H. Bussey.
1994.
Characterization of the yeast (16)--glucan biosynthetic components, Kre6p and Skn1p, and genetic interactions between the PKC1 pathway and extracellular matrix assembly.
J. Cell Biol.
127:567-579 |
| 177. |
Ross-Macdonald, P.,
A. Sheehan,
G. S. Roeder, and M. Snyder.
1997.
A multipurpose transposon system for analyzing protein production, localization, and function in Saccharomyces cerevisiae.
Proc. Natl. Acad. Sci. USA
94:190-195 |
| 178. |
Roth, A. F., and N. G. Davis.
1996.
Ubiquitination of the yeast a-factor receptor.
J. Cell Biol.
134:661-674 |
| 178a. | Samejima, I., S. Mackie, and P. A. Fantes. 1997. Multiple modes of activation of the stress-responsive MAP kinase pathway in fission yeast. EMBO J. 16:6162-6170[Medline]. |
| 179. | Schlessinger, J. 1994. SH2/SH3 signalling proteins. Curr. Opin. Genet. Dev. 4:25-30[Medline]. |
| 180. | Schmidt, A., M. Bickle, T. Beck, and M. N. Hall. 1997. The yeast phosphatidylinositol kinase homolog Tor2 activates Rho1 and Rho2 via the exchange factor Rom2. Cell 88:531-542[Medline]. |
| 181. | Schüller, C., J. L. Brewster, M. R. Alexander, M. C. Gustin, and H. Ruis. 1994. The HOG pathway controls osmotic regulation of transcription via the stress response element (STRE) of the Saccharomyces cerevisiae CTT1 gene. EMBO J. 13:4382-4389[Medline]. |
| 182. | Schumacher, M. M., C. S. Enderlin, and C. P. Selitrennikoff. 1997. The osmotic-1 locus of Neurospora crassa encodes a putative histidine kinase similar to osmosensors of bacteria and yeast. Curr. Microbiol. 34:340-347[Medline]. |
| 183. | Seger, R., and W. G. Krebs. 1995. The MAPK signaling cascade. FASEB J. 9:726-735[Abstract]. |
| 184. | Sells, M. A., and J. Chernoff. 1997. Emerging from the PAK: the p21-activated protein kinase family. Trends Cell Biol. 7:162-167. |
| 185. | Sells, M. A., U. G. Knaus, S. Bagrodia, D. M. Ambrose, G. M. Bokoch, and J. Chernoff. 1997. Human p21-activated kinase (Pak1) regulates actin organization in mammalian cells. Curr. Biol. 7:202-210. |
| 186. |
Shalon, D.,
S. J. Smith, and P. D. Brown.
1996.
A DNA microarray system for analyzing complex DNA samples using two-color fluorescent probe hybridization.
Genome Res.
6:639-645 |
| 187. |
Shieh, J.-C.,
M. G. Wilkinson,
V. Buck,
B. A. Morgan,
K. Makino, and J. B. A. Millar.
1997.
The Mcs4 response regulator coordinately controls the stress-activated Wak1-Wis1-Sty MAP kinase pathway and fission yeast cell cycle.
Genes Dev.
11:1008-1022 |
| 188. | Shiozaki, K., M. Shiozaki, and P. Russell. 1997. Mcs4 mitotic catastrophe suppressor regulates the fission yeast cell cycle through the Wik1-Wis1-Spc1 kinase cascade. Mol. Biol. Cell 8:409-419[Abstract]. |
| 189. |
Shiozaki, K., and P. Russell.
1996.
Conjugation, meiosis, and the osmotic stress response are regulated by Spc1 kinase through Atf1 transcription factor in fission yeast.
Genes Dev.
10:2276-2288 |
| 190. | Shiozaki, K., and P. Russell. 1995. Cell-cycle control linked to extracellular environment by a MAP kinase pathway in fission yeast. Nature 378:739-743[Medline]. |
| 191. | Siderovski, D. P., A. Hessel, S. Chung, T. W. Mak, and M. Tyers. 1996. A new family of regulators of G-protein-coupled receptors? Curr. Biol. 6:211-212[Medline]. |
| 192. | Sietsma, H. H., and J. G. H. Wessels. 1994. Apical wall biogenesis, p. 125-141. In J. G. H. Wessels, and F. Meinhardt (ed.), The Mycota, vol. 1. Springer-Verlag KG, Heidelberg, Germany. |
| 193. | Simon, M. N., C. de Virgilio, B. Souza, J. R. Pringle, A. Abo, and S. I. Reed. 1995. Role for the Rho-family GTPase Cdc42 in yeast mating-pheromone signal pathway. Nature 376:702-705[Medline]. |
| 194. |
Song, O. K.,
J. W. Dolan,
Y. O. Yuan, and S. Fields.
1991.
Pheromone-dependent phosphorylation of the yeast STE12 protein correlates with transcriptional activation.
Genes Dev.
5:741-750 |
| 195. | Spellig, T., M. Bölker, F. Lottspeich, R. W. Frank, and R. Kahmann. 1994. Pheromones trigger filamentous growth in Ustilago maydis. EMBO J. 13:1620-1627[Medline]. |
| 196. |
Stankis, M. M.,
C. A. Specht,
H. L. Yang,
L. Giasson,
R. C. Ullrich, and C. P. Novotny.
1992.
The A mating locus of Schizophyllum commune encodes two dissimilar multiallelic homeodomain proteins.
Proc. Natl. Acad. Sci. USA
89:7169-7173 |
| 197. |
Stefan, C. J., and K. J. Blumer.
1994.
The third cytoplasmic loop of a yeast G-protein-coupled receptor controls pathway activation, ligand discrimination, and receptor internalization.
Mol. Cell. Biol.
14:3339-3349 |
| 198. | Stevenson, B. J., N. Rhodes, B. Errede, and G. F. Sprague. 1992. Constitutive mutants of the protein kinase Ste11 activate the yeast pheromone response pathway in the absence of the G protein. Genes Dev. 6:1292-1304. |
| 199. |
Sugimoto, A.,
Y. Iino,
T. Maeda,
Y. Watanabe, and M. Yamamoto.
1991.
Schizosaccharomyces pombe ste11+ encodes a transcription factor with an HMG motif that is a critical regulator of sexual development.
Genes Dev.
5:1990-1999 |
| 200. | Takeda, T., T. Toda, K.-I. Kominami, A. Kohnosu, M. Yanagida, and N. Jones. 1995. Schizosaccharomyces pombe atf1+ encodes a transcription factor required for sexual development and entry into stationary phase. EMBO J. 14:6193-6208[Medline]. |
| 201. | Takekawa, M., F. Posas, and H. Saito. 1997. A human homolog of the yeast Ssk2/Ssk22 MAP kinase kinase kinases, MTK1, mediates stress-induced activation of the p38 and JNK pathways. EMBO J. 16:4973-4982[Medline]. |
| 202. |
Tanaka, K.,
J. Davey,
Y. Imai, and M. Yamamoto.
1993.
Schizosaccharomyces pombe map3+ encodes the putative M-factor receptor.
Mol. Cell. Biol.
13:80-88 |
| 203. | Tapon, N., and A. Hall. 1997. Rho, Rac, and Cdc42 GTPases regulate the organization of the actin cytoskeleton. Curr. Opin. Cell. Biol. 9:86-92[Medline]. |
| 204. | Tedford, K., S. Kim, D. Sa, K. Stevens, and M. Tyers. 1997. Regulation of the mating pheromone and invasive growth responses in yeast by two MAP kinase substrates. Curr. Biol. 7:228-238[Medline]. |
| 205. |
Toda, T.,
M. Shimanuki, and M. Yanagida.
1991.
Fission yeast genes that confer resistance to staurosporine encode an AP-1-like transcription factor and a protein kinase related to the mammalian ERK1/MAP2 and budding yeast Fus3 and Kss1 kinases.
Genes Dev.
5:60-73 |
| 206. | Torres, L., H. Martín, M. I. García-Saez, J. Arroyo, M. Molina, M. Sánchez, and C. Nombela. 1991. A protein kinase gene complements the lytic phenotype of Saccharomyces cerevisiae lyt2 mutants. Mol. Microbiol. 5:2845-2854[Medline]. |
| 207. |
Towsend, G. F., and C. C. Lindegren.
1954.
Characteristic growth patterns of the different members of a polyploid series of Saccharomyces cerevisiae.
J. Bacteriol.
67:480-483 |
| 208. | Treisman, R. 1996. Regulation of transcription by MAP kinase cascades. Curr. Opin. Cell Biol. 8:205-215[Medline]. |
| 209. |
Vaillancourt, L. J.,
M. Raudaskoski,
C. A. Specht, and C. A. Raper.
1997.
Multiple genes encoding pheromones and a pheromone receptor define the B1 mating-type specificity in Schizophyllum commune.
Genetics
146:541-554[Abstract].
|
| 210. | Vaillancourt, L. J., and C. A. Raper. 1996. Pheromones and pheromone receptors as mating-type determinants in Basidiomycetes, p. 219-247. In J. K. Setlow (ed.), Genetic engineering, vol. 18. Plenum Press, New York, N.Y. |
| 211. | Varela, J. C. S., U. M. Praekelt, P. A. Meacock, R. J. Planta, and W. H. Mager. 1995. The Saccharomyces cerevisiae HSP12 gene is activated by the high-osmolarity glycerol pathway and negatively regulated by protein kinase A. Mol. Cell. Biol. 15:6232-6245[Abstract]. |
| 212. | Varela, J. C. S., C. A. van Beekvelt, R. J. Planta, and W. H. Mager. 1992. Osmostress-induced changes in yeast gene expression. Mol. Microbiol. 6:2183-2190[Medline]. |
| 213. |
Wang, Y.,
H.-P. Xu,
M. Riggs,
L. Rodgers, and M. Wigler.
1991.
byr2, a Schizosaccharomyces pombe gene encoding a protein kinase capable of partial suppression of the ras1 mutant phenotype.
Mol. Cell. Biol.
11:3554-3563 |
| 214. |
Wang, Z.,
P. C. Harkins,
R. J. Ulevitch,
J. Han,
M. H. Cobb, and E. J. Goldsmith.
1997.
The structure of mitogen-activated protein kinase p38 at 2.1 Å resolution.
Proc. Natl. Acad. Sci. USA
94:2327-2332 |
| 215. | Warbrick, E., and P. A. Fantes. 1991. The Wis1 protein kinase is a dosage-dependent regulator of mitosis in Schizosaccharomyces pombe. EMBO J. 13:4291-4299[Medline]. |
| 216. | Ward, M. P., C. J. Gimeno, G. R. Fink, and S. Garrett. 1995. SOK2 may regulate cyclic AMP-dependent protein kinase-stimulated growth and pseudohyphal development by repressing transcription. Mol. Cell. Biol. 15:6854-6863[Abstract]. |
| 217. | Watanabe, Y., G. Takaesu, M. Hagiwara, K. Irie, and K. Matsumoto. 1997. Characterization of a serum response factor-like protein in Saccharomyces cerevisiae, Rlm1, which has transcriptional activity regulated by the Mpk1 (Slt2) mitogen-activated protein kinase pathway. Mol. Cell. Biol. 17:2615-2623[Abstract]. |
| 218. | Watanabe, Y., K. Irie, and K. Matsumoto. 1995. Yeast RLM1 encodes a serum response factor-like protein that may function downstream of the Mpk1 (Slt2) mitogen-activated protein kinase pathway. Mol. Cell. Biol. 15:5740-5749[Abstract]. |
| 219. | Watanabe, Y., Y. Iino, K. Furuhata, C. Shimoda, and M. Yamamoto. 1988. The S. pombe mei2 gene encoding a crucial molecule for commitment to meiosis is under the regulation of cAMP. EMBO J. 7:761-767[Medline]. |
| 220. |
Wendland, J.,
L. J. Vaillancourt,
J. Hegner,
K. B. Lengeler,
K. J. Laddison,
C. A. Specht,
C. A. Raper, and E. Kothe.
1995.
The mating type locus B1 of Schizophyllum commune contains a pheromone receptor gene and putative pheromone genes.
EMBO J.
14:5271-5278[Medline].
|
| 221. |
Whiteway, M. S.,
C. Wu,
T. Leeuw,
K. Clark,
A. Fourest-Lieuvin,
D. Y. Thomas, and E. Leberer.
1995.
Association of the yeast pheromone response G protein subunits with the MAP kinase scaffold Ste5p.
Science
269:1572-1575 |
| 222. |
Wilkinson, M. G.,
M. Samuels,
T. Takeda,
W. M. Toone,
J.-C. Shieh,
T. Toda,
J. B. A. Millar, and N. Jones.
1996.
The Atf1 transcription factor is a target for the Sty1 stress-activated MAP kinase pathway in fission yeast.
Genes Dev.
10:2289-2301 |
| 223. | Willer, M., L. Hoffmann, U. Styrkársdóttir, R. Egel, J. Davey, and O. Nielsen. 1995. Two-step activation of meiosis by the mat1 locus in Schizosaccharomyces pombe. Mol. Cell. Biol. 15:4964-4970[Abstract]. |
| 224. |
Wu, C.,
M. Whiteway,
D. Y. Thomas, and E. Leberer.
1995.
Molecular characterization of Ste20p, a potential mitogen-activated protein extracellular signal-regulated kinase kinase (MEK) kinase kinase from Saccharomyces cerevisiae.
J. Biol. Chem.
270:15984-15992 |
| 225. |
Xu, J. R., and J. E. Hamer.
1996.
MAP kinase and cAMP signaling regulate infection structure formation and pathogenic growth in the rice blast fungus Magnaporthe grisea.
Genes Dev.
10:2696-2706 |
| 226. | Yabana, N., and M. Yamamoto. 1996. Schizosaccharomyces pombe map1+ encodes a MADS-box-family protein required for cell-type specific gene expression. Mol. Cell. Biol. 16:3420-3428[Abstract]. |
| 227. |
Yablonski, D.,
I. Marbach, and A. Levitzki.
1996.
Dimerization of Ste5, a mitogen-activated protein kinase cascade scaffold protein, is required for signal transduction.
Proc. Natl. Acad. Sci. USA
93:13864-13869 |
| 228. | Yamamoto, M. 1996. The molecular control mechanisms of meiosis in fission yeast. Trends Biochem. 21:18-22[Medline]. |
| 228a. | Yamamoto, M., Y. Imai, and Y. Watanabe. 1997. Mating and sporulation in Schizosaccharomyces pombe, p. 1037-1106. In J. R. Pringle, J. R. Broach, and E. W. Jones (ed.), The molecular and cellular biology of the yeast Saccharomyces. Cell cycle and cell biology, vol. 3. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. |
| 229. |
Yamochi, W.,
K. Tanaka,
H. Nonaka,
A. Maeda,
T. Musha, and Y. Takai.
1994.
Growth site localization of Rho1 small GTP-binding protein and its involvement in bud formation in Saccharomyces cerevisiae.
J. Cell Biol.
125:1077-1093 |
| 230. | Zarzov, P., C. Mazzoni, and C. Mann. 1996. The Slt2 (Mpk1) MAP kinase is activated during periods of polarized cell growth in yeast. EMBO J. 15:83-91[Medline]. |
| 231. | Zhan, X. L., R. J. Deschenes, and K. L. Guan. 1997. Differential regulation of Fus3 MAP kinase by tyrosine-specific phosphatases Ptp2/Ptp3 and dual-specificity phosphatase Msg5 in Saccharomyces cerevisiae. Genes Dev. 13:1690-1702. |
| 232. | Zhang, F., A. Strand, D. Robbins, M. H. Cobb, and E. J. Goldsmith. 1994. Atomic structure of the MAP kinase ERK2 at 2.3 Å resolution. Nature 367:704-711[Medline]. |
| 233. | Zhao, Z.-S., T. Leung, E. Manser, and L. Lim. 1995. Pheromone signalling in Saccharomyces cerevisiae requires the small GTP-binding protein Cdc42p and its activator Cdc24. Mol. Cell. Biol. 15:5246-5257[Abstract]. |
| 234. |
Zheng, Y.,
M. J. Hart,
K. Shinip,
T. Evans,
A. Bender, and R. A. Cerione.
1993.
Biochemical comparisons of the Saccharomyces cerevisiae Bem2 and Bem3 proteins.
J. Biol. Chem.
268:24629-24634 |
| 235. |
Zhou, Z.,
A. Gartner,
R. Cade,
G. Ammerer, and B. Errede.
1993.
Pheromone-induced signal transduction in Saccharomyces cerevisiae requires the sequential function of three protein kinases.
Mol. Cell. Biol.
13:2069-2080 |
Microbiol Mol Biol Rev, June 1998, p. 249-274, Vol. 62, No. 2
1092-2172/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
This article has been cited by other articles:
-
Atoui, A., Bao, D., Kaur, N., Grayburn, W. S., Calvo, A. M.
(2008). Aspergillus nidulans Natural Product Biosynthesis Is Regulated by MpkB, a Putative Pheromone Response Mitogen-Activated Protein Kinase. Appl. Environ. Microbiol.
74: 3596-3600
[Abstract] [Full Text] -
Yi, S., Sahni, N., Daniels, K. J., Pujol, C., Srikantha, T., Soll, D. R.
(2008). The Same Receptor, G Protein, and Mitogen-activated Protein Kinase Pathway Activate Different Downstream Regulators in the Alternative White and Opaque Pheromone Responses of Candida albicans. Mol. Biol. Cell
19: 957-970
[Abstract] [Full Text] -
Segmuller, N., Ellendorf, U., Tudzynski, B., Tudzynski, P.
(2007). BcSAK1, a Stress-Activated Mitogen-Activated Protein Kinase, Is Involved in Vegetative Differentiation and Pathogenicity in Botrytis cinerea. Eukaryot Cell
6: 211-221
[Abstract] [Full Text] -
Heiman, M. G., Engel, A., Walter, P.
(2007). The Golgi-resident protease Kex2 acts in conjunction with Prm1 to facilitate cell fusion during yeast mating. JCB
176: 209-222
[Abstract] [Full Text] -
Wu, C., Jansen, G., Zhang, J., Thomas, D. Y., Whiteway, M.
(2006). Adaptor protein Ste50p links the Ste11p MEKK to the HOG pathway through plasma membrane association.. Genes Dev.
20: 734-746
[Abstract] [Full Text] -
James, T. Y., Srivilai, P., Kues, U., Vilgalys, R.
(2006). Evolution of the Bipolar Mating System of the Mushroom Coprinellus disseminatus From Its Tetrapolar Ancestors Involves Loss of Mating-Type-Specific Pheromone Receptor Function. Genetics
172: 1877-1891
[Abstract] [Full Text] -
Jin, Y., Weining, S., Nevo, E.
(2005). A MAPK gene from Dead Sea fungus confers stress tolerance to lithium salt and freezing-thawing: Prospects for saline agriculture. Proc. Natl. Acad. Sci. USA
102: 18992-18997
[Abstract] [Full Text] -
Roman, E., Nombela, C., Pla, J.
(2005). The Sho1 Adaptor Protein Links Oxidative Stress to Morphogenesis and Cell Wall Biosynthesis in the Fungal Pathogen Candida albicans. Mol. Cell. Biol.
25: 10611-10627
[Abstract] [Full Text] -
Kayingo, G., Wong, B.
(2005). The MAP kinase Hog1p differentially regulates stress-induced production and accumulation of glycerol and D-arabitol in Candida albicans. Microbiology
151: 2987-2999
[Abstract] [Full Text] -
Arana, D. M., Nombela, C., Alonso-Monge, R., Pla, J.
(2005). The Pbs2 MAP kinase kinase is essential for the oxidative-stress response in the fungal pathogen Candida albicans. Microbiology
151: 1033-1049
[Abstract] [Full Text] -
Vilella, F., Herrero, E., Torres, J., de la Torre-Ruiz, M. A.
(2005). Pkc1 and the Upstream Elements of the Cell Integrity Pathway in Saccharomyces cerevisiae, Rom2 and Mtl1, Are Required for Cellular Responses to Oxidative Stress. J. Biol. Chem.
280: 9149-9159
[Abstract] [Full Text] -
Ganem, S., Lu, S.-W., Lee, B.-N., Chou, D. Y.-T., Hadar, R., Turgeon, B. G., Horwitz, B. A.
(2004). G-Protein {beta} Subunit of Cochliobolus heterostrophus Involved in Virulence, Asexual and Sexual Reproductive Ability, and Morphogenesis. Eukaryot Cell
3: 1653-1663
[Abstract] [Full Text] -
Sussman, A., Huss, K., Chio, L.-C., Heidler, S., Shaw, M., Ma, D., Zhu, G., Campbell, R. M., Park, T.-S., Kulanthaivel, P., Scott, J. E., Carpenter, J. W., Strege, M. A., Belvo, M. D., Swartling, J. R., Fischl, A., Yeh, W.-K., Shih, C., Ye, X. S.
(2004). Discovery of Cercosporamide, a Known Antifungal Natural Product, as a Selective Pkc1 Kinase Inhibitor through High-Throughput Screening. Eukaryot Cell
3: 932-943
[Abstract] [Full Text] -
Pandey, A., Roca, M. G., Read, N. D., Glass, N. L.
(2004). Role of a Mitogen-Activated Protein Kinase Pathway during Conidial Germination and Hyphal Fusion in Neurospora crassa. Eukaryot Cell
3: 348-358
[Abstract] [Full Text] -
Smith, D. G., Garcia-Pedrajas, M. D., Hong, W., Yu, Z., Gold, S. E., Perlin, M. H.
(2004). An ste20 Homologue in Ustilago maydis Plays a Role in Mating and Pathogenicity. Eukaryot Cell
3: 180-189
[Abstract] [Full Text] -
Grimshaw, S. J., Mott, H. R., Stott, K. M., Nielsen, P. R., Evetts, K. A., Hopkins, L. J., Nietlispach, D., Owen, D.
(2004). Structure of the Sterile {alpha} Motif (SAM) Domain of the Saccharomyces cerevisiae Mitogen-activated Protein Kinase Pathway-modulating Protein STE50 and Analysis of Its Interaction with the STE11 SAM. J. Biol. Chem.
279: 2192-2201
[Abstract] [Full Text] -
Muller, P., Weinzierl, G., Brachmann, A., Feldbrugge, M., Kahmann, R.
(2003). Mating and Pathogenic Development of the Smut Fungus Ustilago maydis Are Regulated by One Mitogen-Activated Protein Kinase Cascade. Eukaryot Cell
2: 1187-1199
[Abstract] [Full Text] -
Noble, B., Kallal, L. A., Pausch, M. H., Benovic, J. L.
(2003). Development of a Yeast Bioassay to Characterize G Protein-coupled Receptor Kinases: IDENTIFICATION OF AN NH2-TERMINAL REGION ESSENTIAL FOR RECEPTOR PHOSPHORYLATION. J. Biol. Chem.
278: 47466-47476
[Abstract] [Full Text] -
Wu, C., Arcand, M., Jansen, G., Zhong, M., Iouk, T., Thomas, D. Y., Meloche, S., Whiteway, M.
(2003). Phosphorylation of the MAPKKK Regulator Ste50p in Saccharomyces cerevisiae: a Casein Kinase I Phosphorylation Site Is Required for Proper Mating Function. Eukaryot Cell
2: 949-961
[Abstract] [Full Text] -
Braus, G. H., Grundmann, O., Bruckner, S., Mosch, H.-U.
(2003). Amino Acid Starvation and Gcn4p Regulate Adhesive Growth and FLO11 Gene Expression in Saccharomyces cerevisiae. Mol. Biol. Cell
14: 4272-4284
[Abstract] [Full Text] -
Kelley, B. P., Sharan, R., Karp, R. M., Sittler, T., Root, D. E., Stockwell, B. R., Ideker, T.
(2003). Conserved pathways within bacteria and yeast as revealed by global protein network alignment. Proc. Natl. Acad. Sci. USA
100: 11394-11399
[Abstract] [Full Text] -
Horak, C. E., Luscombe, N. M., Qian, J., Bertone, P., Piccirrillo, S., Gerstein, M., Snyder, M.
(2002). Complex transcriptional circuitry at the G1/S transition in Saccharomyces cerevisiae. Genes Dev.
16: 3017-3033
[Abstract] [Full Text] -
Akal-Strader, A., Khare, S., Xu, D., Naider, F., Becker, J. M.
(2002). Residues in the First Extracellular Loop of a G Protein-coupled Receptor Play a Role in Signal Transduction. J. Biol. Chem.
277: 30581-30590
[Abstract] [Full Text] -
Rocha-Ramirez, V., Omero, C., Chet, I., Horwitz, B. A., Herrera-Estrella, A.
(2002). Trichoderma atroviride G-Protein {alpha}-Subunit Gene tga1 Is Involved in Mycoparasitic Coiling and Conidiation. Eukaryot Cell
1: 594-605
[Abstract] [Full Text] -
Rodriguez-Pachon, J. M., Martin, H., North, G., Rotger, R., Nombela, C., Molina, M.
(2002). A Novel Connection between the Yeast Cdc42 GTPase and the Slt2-mediated Cell Integrity Pathway Identified through the Effect of Secreted Salmonella GTPase Modulators. J. Biol. Chem.
277: 27094-27102
[Abstract] [Full Text] -
Hohmann, S.
(2002). Osmotic Stress Signaling and Osmoadaptation in Yeasts. Microbiol. Mol. Biol. Rev.
66: 300-372
[Abstract] [Full Text] -
Shen, W.-C., Davidson, R. C., Cox, G. M., Heitman, J.
(2002). Pheromones Stimulate Mating and Differentiation via Paracrine and Autocrine Signaling in Cryptococcus neoformans. Eukaryot Cell
1: 366-377
[Abstract] [Full Text] -
Chung, S., Karos, M., Chang, Y. C., Lukszo, J., Wickes, B. L., Kwon-Chung, K. J.
(2002). Molecular Analysis of CPR{alpha}, a MAT{alpha}-Specific Pheromone Receptor Gene of Cryptococcus neoformans. Eukaryot Cell
1: 432-439
[Abstract] [Full Text] -
Chai, B., Hsu, J.-m., Du, J., Laurent, B. C.
(2002). Yeast RSC Function Is Required for Organization of the Cellular Cytoskeleton via an Alternative PKC1 Pathway. Genetics
161: 575-584
[Abstract] [Full Text] -
Sanchez-Piris, M., Posas, F., Alemany, V., Winge, I., Hidalgo, E., Bachs, O., Aligue, R.
(2002). The Serine/Threonine Kinase Cmk2 Is Required for Oxidative Stress Response in Fission Yeast. J. Biol. Chem.
277: 17722-17727
[Abstract] [Full Text] -
Taricani, L., Tejada, M. L., Young, P. G.
(2002). The Fission Yeast ES2 Homologue, Bis1, Interacts with the Ish1 Stress-responsive Nuclear Envelope Protein. J. Biol. Chem.
277: 10562-10572
[Abstract] [Full Text] -
Boyce, K. J., Hynes, M. J., Andrianopoulos, A.
(2001). The CDC42 Homolog of the Dimorphic Fungus Penicillium marneffei Is Required for Correct Cell Polarization during Growth but Not Development. J. Bacteriol.
183: 3447-3457
[Abstract] [Full Text] -
Bolker, M.
(2001). Ustilago maydis - a valuable model system for the study of fungal dimorphism and virulence. Microbiology
147: 1395-1401
[Full Text] -
Nanduri, J., Tartakoff, A. M.
(2001). Perturbation of the Nucleus: A Novel Hog1p-independent, Pkc1p-dependent Consequence of Hypertonic Shock in Yeast. Mol. Biol. Cell
12: 1835-1841
[Abstract] [Full Text] -
Smits, G. J., van den Ende, H., Klis, F. M.
(2001). Differential regulation of cell wall biogenesis during growth and development in yeast. Microbiology
147: 781-794
[Full Text] -
Cebolla, A., Sousa, C., Lorenzo, V. d.
(2001). Rational design of a bacterial transcriptional cascade for amplifying gene expression capacity. Nucleic Acids Res
29: 759-766
[Abstract] [Full Text] -
Shimizu, K., Keller, N. P.
(2001). Genetic Involvement of a cAMP-Dependent Protein Kinase in a G Protein Signaling Pathway Regulating Morphological and Chemical Transitions in Aspergillus nidulans. Genetics
157: 591-600
[Abstract] [Full Text] -
Alexander, M. R., Tyers, M., Perret, M., Craig, B. M., Fang, K. S., Gustin, M. C.
(2001). Regulation of Cell Cycle Progression by Swe1p and Hog1p Following Hypertonic Stress. Mol. Biol. Cell
12: 53-62
[Abstract] [Full Text] -
Lengeler, K. B., Davidson, R. C., D'souza, C., Harashima, T., Shen, W.-C., Wang, P., Pan, X., Waugh, M., Heitman, J.
(2000). Signal Transduction Cascades Regulating Fungal Development and Virulence. Microbiol. Mol. Biol. Rev.
64: 746-785
[Abstract] [Full Text] -
Cullen, P. J., Sprague, G. F. Jr.
(2000). Glucose depletion causes haploid invasive growth in yeast. Proc. Natl. Acad. Sci. USA
10.1073/pnas.240345197v1
[Abstract] [Full Text] -
Palecek, S. P., Parikh, A. S., Kron, S. J.
(2000). Genetic Analysis Reveals That FLO11 Upregulation and Cell Polarization Independently Regulate Invasive Growth in Saccharomyces cerevisiae. Genetics
156: 1005-1023
[Abstract] [Full Text] -
Kim, M., Lee, W., Park, J., Kim, J. B., Jang, Y. K., Seong, R. H., Choe, S. Y., Park, S. D.
(2000). The stress-activated MAP kinase Sty1/Spc1 and a 3'-regulatory element mediate UV-induced expression of the uvi15+ gene at the post-transcriptional level. Nucleic Acids Res
28: 3392-3402
[Abstract] [Full Text] -
Ernst, J. F.
(2000). Transcription factors in Candida albicans - environmental control of morphogenesis. Microbiology
146: 1763-1774
[Full Text] -
Nguyen, A. N., Lee, A., Place, W., Shiozaki, K.
(2000). Multistep Phosphorelay Proteins Transmit Oxidative Stress Signals to the Fission Yeast Stress-activated Protein Kinase. Mol. Biol. Cell
11: 1169-1181
[Abstract] [Full Text] -
Calera, J. A., Zhao, X.-J., Calderone, R.
(2000). Defective Hyphal Development and Avirulence Caused by a Deletion of the SSK1 Response Regulator Gene in Candida albicans. Infect. Immun.
68: 518-525
[Abstract] [Full Text] -
Inagaki, M., Schmelzle, T., Yamaguchi, K., Irie, K., Hall, M. N., Matsumoto, K.
(1999). PDK1 Homologs Activate the Pkc1-Mitogen-Activated Protein Kinase Pathway in Yeast. Mol. Cell. Biol.
19: 8344-8352
[Abstract] [Full Text] -
Yue, C., Cavallo, L. M., Alspaugh, J. A., Wang, P., Cox, G. M., Perfect, J. R., Heitman, J.
(1999). The STE12{alpha} Homolog Is Required for Haploid Filamentation But Largely Dispensable for Mating and Virulence in Cryptococcus neoformans. Genetics
153: 1601-1615
[Abstract] [Full Text] -
Lev, S., Sharon, A., Hadar, R., Ma, H., Horwitz, B. A.
(1999). A mitogen-activated protein kinase of the corn leaf pathogen Cochliobolus heterostrophus is involved in conidiation, appressorium formation, and pathogenicity: Diverse roles for mitogen-activated protein kinase homologs in foliar pathogens. Proc. Natl. Acad. Sci. USA
96: 13542-13547
[Abstract] [Full Text] -
Davenport, K. D., Williams, K. E., Ullmann, B. D., Gustin, M. C.
(1999). Activation of the Saccharomyces cerevisiae Filamentation/Invasion Pathway by Osmotic Stress in High-Osmolarity Glycogen Pathway Mutants. Genetics
153: 1091-1103
[Abstract] [Full Text] -
Delley, P.-A., Hall, M. N.
(1999). Cell Wall Stress Depolarizes Cell Growth Via Hyperactivation of RHO1. JCB
147: 163-174
[Abstract] [Full Text] -
Dixon, K. P., Xu, J.-R., Smirnoff, N., Talbot, N. J.
(1999). Independent Signaling Pathways Regulate Cellular Turgor during Hyperosmotic Stress and Appressorium-Mediated Plant Infection by Magnaporthe grisea. Plant Cell
11: 2045-2058
[Abstract] [Full Text] -
Ahn, S.-H., Acurio, A., Kron, S. J.
(1999). Regulation of G2/M Progression by the STE Mitogen-activated Protein Kinase Pathway in Budding Yeast Filamentous Growth. Mol. Biol. Cell
10: 3301-3316
[Abstract] [Full Text] -
Wu, C., Leberer, E., Thomas, D. Y., Whiteway, M.
(1999). Functional Characterization of the Interaction of Ste50p with Ste11p MAPKKK in Saccharomyces cerevisiae. Mol. Biol. Cell
10: 2425-2440
[Abstract] [Full Text] -
Ketela, T., Green, R., Bussey, H.
(1999). Saccharomyces cerevisiae Mid2p Is a Potential Cell Wall Stress Sensor and Upstream Activator of the PKC1-MPK1 Cell Integrity Pathway. J. Bacteriol.
181: 3330-3340
[Abstract] [Full Text] -
Monge, R. A., Navarro-García, F., Molero, G., Diez-Orejas, R., Gustin, M., Pla, J., Sánchez, M., Nombela, C.
(1999). Role of the Mitogen-Activated Protein Kinase Hog1p in Morphogenesis and Virulence of Candida albicans. J. Bacteriol.
181: 3058-3068
[Abstract] [Full Text] -
Jia, Z., Young, P. G.
(1999). Ssp1 Promotes Actin Depolymerization and Is Involved in Stress Response and New End Take-Off Control in Fission Yeast. Mol. Biol. Cell
10: 1495-1510
[Abstract] [Full Text] -
Johnson, D. I.
(1999). Cdc42: An Essential Rho-Type GTPase Controlling Eukaryotic Cell Polarity. Microbiol. Mol. Biol. Rev.
63: 54-105
[Abstract] [Full Text] -
Longtine, M. S., Fares, H., Pringle, J. R.
(1998). Role of the Yeast Gin4p Protein Kinase in Septin Assembly and the Relationship between Septin Assembly and Septin Function. JCB
143: 719-736
[Abstract] [Full Text] -
Xu, J.-R., Staiger, C. J., Hamer, J. E.
(1998). Inactivation of the mitogen-activated protein kinase Mps1 from the rice blast fungus prevents penetration of host cells but allows activation of plant defense responses. Proc. Natl. Acad. Sci. USA
95: 12713-12718
[Abstract] [Full Text] -
O'Rourke, S. M., Herskowitz, I.
(1998). The Hog1 MAPK prevents cross talk between the HOG and pheromone response MAPK pathways in Saccharomyces cerevisiae. Genes Dev.
12: 2874-2886
[Abstract] [Full Text] -
Cullen, P. J., Sprague, G. F. Jr.
(2000). Glucose depletion causes haploid invasive growth in yeast. Proc. Natl. Acad. Sci. USA
97: 13619-13624
[Abstract] [Full Text]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»