KAT2A, or GCN5, is a histone acetyltransferase (HAT) that functions primarily as a transcriptional activator. Acetylation of histones gives a specific tag for epigenetic transcription activation. In case of HIV-1 infection, it is recruited by the viral protein Tat. Regulates Tat's transactivating activity and may help inducing chromatin remodeling of proviral genes. Component of the SAGA and ATAC complexes, complexes with histone acetyltransferase activities on histones H3 and H4