Functions as component of the transcription regulatory histone acetylation (HAT) complexes SAGA, SALSA and ADA. SAGA is involved in RNA polymerase II-dependent transcriptional regulation of approximately 10% of yeast genes. At the promoters, SAGA is required for recruitment of the basal transcription machinery. It influences RNA polymerase II transcriptional activity through different activities such as TBP interaction (SPT3, SPT8 and SPT20) and promoter selectivity, interaction with transcription activators (GCN5, ADA2, ADA3 and TRA1), and chromatin modification through histone acetylation (GCN5) and deubiquitination (UBP8). SAGA acetylates nucleosomal histone H3 to some extent (to form H3K9ac, H3K14ac, H3K18ac and H3K23ac). SAGA interacts with DNA via upstream activating sequences (UASs). SALSA, an altered form of SAGA, may be involved in positive transcriptional regulation. SLIK is proposed to have partly overlapping functions with SAGA. It preferentially acetylates methylated histone H3, at least after activation at the GAL1-10 locus. ADA preferentially acetylates nucleosomal histones H3 (to form H3K14ac and H3K18ac) and H2B.