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Microbiology and Molecular Biology Reviews, June 2006, p. 472-509, Vol. 70, No. 2
1092-2172/06/$08.00+0 doi:10.1128/MMBR.00046-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Department of Basic Medical Sciences, Biochemistry Section, University of the West Indies, Mona Campus, Kingston 7, Jamaica,1 Ecole Normale Supérieure, CNRS UMR 8541, Génétique Moléculaire, 46 rue d'Ulm, 75230 Paris Cedex 05, France2
A survey of the already characterized and potential two-component protein sequences that exist in the nine complete and seven partially annotated cyanobacterial genome sequences available (as of May 2005) showed that the cyanobacteria possess a much larger repertoire of such proteins than most other bacteria. By analysis of the domain structure of the 1,171 potential histidine kinases, response regulators, and hybrid kinases, many various arrangements of about thirty different modules could be distinguished. The number of two-component proteins is related in part to genome size but also to the variety of physiological properties and ecophysiologies of the different strains. Groups of orthologues were defined, only a few of which have representatives with known physiological functions. Based on comparisons with the proposed phylogenetic relationships between the strains, the orthology groups show that (i) a few genes, some of them clustered on the genome, have been conserved by all species, suggesting their very ancient origin and an essential role for the corresponding proteins, and (ii) duplications, fusions, gene losses, insertions, and deletions, as well as domain shuffling, occurred during evolution, leading to the extant repertoire. These mechanisms are put in perspective with the different genetic properties that cyanobacteria have to achieve genome plasticity. This review is designed to serve as a basis for orienting further research aimed at defining the most ancient regulatory mechanisms and understanding how evolution worked to select and keep the most appropriate systems for cyanobacteria to develop in the quite different environments that they have successfully colonized.
Supplemental
material for this article may be found at
http://mmbr.asm.org/.
Present
address: School of Biological and Chemical Sciences, Queen Mary
University of London, Mile End Road, London E1 4NS, United
Kingdom.
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