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)YesH4Yeast HAT-B, HAT-A3 (no nucleosome acetylation)
 Gcn5Various (yeast to humans)Coactivator (adaptor)YesH3/H4Yeast ADA, SAGA (H3/H2B); human GCN5 complex, STAGA, TFTC (H3)
 PCAFHumans, miceCoactivatorYesH3/H4Human PCAF complex (H3/weak H4)
 Elp3YeastTranscript elongationYesND*Elongator, polymerase II holoenzyme (H3/weak H4)
MYST family
 Esa1YeastCell cycle progressionYesH4/H3/H2ANuA4 (H4/H2A)
 MOFDrosophilaDosage compensationYesH4/H3/H2AMSL complex (H4)
 Tip60HumansHIV Tat interactionYesH4/H3/H2ATip60 complex
 MOZHumansLeukemogenesis, upon chromosomal translocationND
 MORFHumansUnknown (strong homology to MOZ)YesH4/H3/H2A
 HBO1HumansORC interactionYes*ND*HBO1 complex
p300/CBPVarious multicellularGlobal coactivatorYesH2A/H2B/H3/H4
Nuclear receptor coactivatorsNuclear receptor coactivators (transcriptional response to hormone signals)
 SRC-1Humans, miceYesH3/H4
 ACTRHumans, miceYesH3/H4
 TIF2Humans, miceND
TAFII250Various (yeast to humans)TBP-associated factorYesH3/H4TFIID
TFIIICRNA polymerase III transcription initiationTFIIIC (H2A/H3/H4)
  • 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  • c S. John and J. L. Workman, unpublished result.