Table 1.

Summary of known and putative HATs

HATOrganisms known to contain the HATKnown transcription-related functions/effectsHAT activity demonstrated in vitrobHistone specificity of recombinant enzyme in vitroa,bKnown native HAT complexes and nucleosomal histone specificities in vitro
GNAT superfamily
 Hat1Various (yeast to humans)None (histone deposition-related B-type HAT)Yes H4 Yeast HAT-B, HAT-A3 (no nucleosome acetylation)
 Gcn5Various (yeast to humans)Coactivator (adaptor)Yes H3/H4Yeast ADA, SAGA (H3/H2B); human GCN5 complex, STAGA, TFTC (H3)
 PCAFHumans, miceCoactivatorYes H3/H4Human PCAF complex (H3/weak H4)
 Elp3YeastTranscript elongationYesND* Elongator, polymerase II holoenzyme (H3/weak H4)
 Hpa2YeastUnknownYes H3/H4
MYST family
 Sas3YeastSilencingYes H3/H4/H2ANuA3c(H3)
 Esa1YeastCell cycle progressionYes H4/H3/H2ANuA4 (H4/H2A)
 MOF Drosophila Dosage compensationYes H4/H3/H2AMSL complex (H4)
 Tip60HumansHIV Tat interactionYes H4/H3/H2ATip60 complex
 MOZHumansLeukemogenesis, upon chromosomal translocationND
 MORFHumansUnknown (strong homology to MOZ)Yes H4/H3/H2A
 HBO1HumansORC interactionYes* ND* HBO1 complex
p300/CBPVarious multicellularGlobal coactivatorYes H2A/H2B/H3/H4
Nuclear receptor coactivatorsNuclear receptor coactivators (transcriptional response to hormone signals)
 SRC-1Humans, miceYes H3/H4
 ACTRHumans, miceYes H3/H4
 TIF2Humans, miceND
TAFII250Various (yeast to humans)TBP-associated factorYes H3/H4TFIID
TFIIICRNA polymerase III transcription initiationTFIIIC (H2A/H3/H4)
 TFIIIC220HumansYes* ND
 TFIIIC90HumansYes H3
  • a Histones that are the primary in vitro substrates for a given HAT are bold; other histones listed are acetylated weakly or in a secondary manner.

  • b Asterisks indicate proteins for which HAT activity has been suggested indirectly or demonstrated in an incomplete manner. Elp3 can acetylate all four histones but has only been tested with them individually in in-gel assays. The HAT function of HBO1 has primarily been shown by the in vitro free histoneH3/H4-acetylating activity of a purified human complex containing it, although recombinant GST-HBO1 (and the complex) did weakly acetylate nucleosomes. Finally, TFIIIC220 was identified as a HAT only in in-gel assays, and its activity has not been confirmed by recombinant protein studies as of this writing. ND, not determined.

  • c S. John and J. L. Workman, unpublished result.