InterPro domain: IPR037800

The transcription regulatory histone acetylation complex Spt-Ada-Gcn5 acetyltransferase (SAGA) is involved in RNA polymerase II-dependent transcriptional regulation of approximately 10% of yeast genes. SAGA preferentially acetylates histones H3 and H2B and deubiquitinates histone H2B [ 1 ]. SAGA is known as PCAF in vertebrates and PCAF acetylates nucleosomal histone H3 [ 2 ]. The SAGA complex consists of at least TRA1, CHD1, SPT7, TAF5, ADA3, SGF73, SPT20/ADA5, SPT8, TAF12, TAF6, HFI1/ADA1, UBP8, GCN5, ADA2, SPT3, SGF29, TAF10, TAF9, SGF11 and SUS1, and some of these components are present as two copies. The complex is built up from distinct modules, each of which has a separate function and crosslinks with either other proteins or other modules in the complex [ 3 ].

SLIK (SAGA-like) is a multi-subunit histone acetyltransferase complex that preferentially acetylates histones H3 and H2B and deubiquitinates histone H2B. It is an embellishment of the SAGA complex. The yeast SLIK complex consists of at least TRA1, CHD1, SPT7, CC TAF5, ADA3, SPT20, RTG2, TAF12, TAF6, HFI1, UBP8 (a deubiquitinase), GCN5, ADA2, SPT3, SGF29, TAF10 and TAF9 [ 4 , 4 ].

The yeast SALSA complex is an altered form of the SAGA complex and consists of at least TRA1, SPT7 (C-terminal truncated form), TAF5, ADA3, SPT20, TAF12, TAF6, HFI1, GCN5, ADA2 and SPT3 [ 5 ].

The ADA complex is a transcription regulatory histone acetylation (HAT) complex. ADA preferentially acetylates nucleosomal histones H3 (at 'Lys-14' and 'Lys-18') and H2B. The complex consists of at least ADA2, ADA3, AHC1, and GCN5. AHC1 is required for the overall structural integrity of the ADA complex [ 6 ].

This entry includes histone acetyltransferases GCN5, KAT2A and KAT2B (all of which are included in 2.3.1.48 ). GCN5 acetylates histones H2B, H3 and H4, providing a specific tag for epigenetic transcription activation. GCN5 is a component of the transcription regulatory histone acetylation (HAT) complexes SAGA [ 7 ], SLIK [ 8 ], SALSA [ 8 ] and ADA [ 8 ]. Mammals have two paralogues: KAT2A (also known as GCN5) and KAT2B. KAT2A acetylates core histones to provide a specific tag for epigenetic transcription activation, but not nucleosome core particles. It also acetylates proteins such as CEBPB [ 9 ]. KAT2A is a component of the ATAC complex, which has acetyltransferase activity on histones H3 and H4 [ 10 ]. KAT2B (also known as P300/calcium-binding protein (CBP)-associated factor or PCAF) can acetylate the core histones H3 and H4 as well as nucleosome core particles and non-histone proteins such as ACLY [ 11 ].

1. Chd1 chromodomain links histone H3 methylation with SAGA- and SLIK-dependent acetylation. Nature 433, 434-8
2. Histone-like TAFs within the PCAF histone acetylase complex. Cell 94, 35-44
3. Architecture of the Saccharomyces cerevisiae SAGA transcription coactivator complex. EMBO J. 33, 2534-46
4. The novel SLIK histone acetyltransferase complex functions in the yeast retrograde response pathway. Mol. Cell. Biol. 22, 8774-86
5. SALSA, a variant of yeast SAGA, contains truncated Spt7, which correlates with activated transcription. Proc. Natl. Acad. Sci. U.S.A. 99, 11622-7
6. Yeast Gcn5 functions in two multisubunit complexes to acetylate nucleosomal histones: characterization of an Ada complex and the SAGA (Spt/Ada) complex. Genes Dev. 11, 1640-50
7. The ATM-related cofactor Tra1 is a component of the purified SAGA complex. Mol. Cell 2, 863-7
8. Expanded lysine acetylation specificity of Gcn5 in native complexes. J. Biol. Chem. 274, 5895-900
9. Glucocorticoid-stimulated preadipocyte differentiation is mediated through acetylation of C/EBPbeta by GCN5. Proc. Natl. Acad. Sci. U.S.A. 104, 2703-8
10. The double-histone-acetyltransferase complex ATAC is essential for mammalian development. Mol. Cell. Biol. 29, 1176-88
11. Acetylation stabilizes ATP-citrate lyase to promote lipid biosynthesis and tumor growth. Mol. Cell 51, 506-18