A multiprotein complex that possesses histone acetyltransferase and is involved in regulation of transcription. Contains either GCN5 or PCAF in a mutually exclusive manner. The budding yeast complex includes Gcn5p, two proteins of the Ada family, and two TBP-associate proteins (TAFs); analogous complexes in other species have analogous compositions, and usually contain homologs of the yeast proteins. Both ATAC- or SAGA (see GO:0000124, SAGA complex) are involved in the acetylation of histone H3K9 and K14 residues.