Essential component of histone acetyltransferase (HAT) complexes, which serves as a target for activators during recruitment of HAT complexes. Essential for vegetative growth. Functions as a component of the transcription regulatory histone acetylation (HAT) complexes SAGA, SALSA and SLIK. 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 and promoter selectivity, interaction with transcription activators, and chromatin modification through histone acetylation and deubiquitination. 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 (By similarity). Component of the SAGA complex. Although strongly related to the PI3/PI4-kinase family, it lacks the typical motifs that constitute the catalytic site of PI3/PI4-kinase proteins, suggesting that it may lack such activity. Belongs to the PI3/PI4-kinase family. TRA1 subfamily.