Histone acetyltransferase (HAT) subunit of the SAS complex, a multiprotein complex that acetylates 'Lys-16' of histone H4 and 'Lys-14' of histone H3. The SAS complex is however unable to acetylate nucleosomal histones. The complex is involved in transcriptional silencing at telomeres and at HML locus. Also involved in rDNA silencing and G0 control. acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] Interacts with CAC1. Component of the SAS complex, at least composed of SAS2, SAS4 and SAS5. These three proteins constitute the core of the complex and are sufficient to acetylate histones. SAS4 is essential for HAT activity of the complex, while SAS5 is required for maxiaml HAT activity. Autoacetylation at Lys-168 is required for proper function. Heterochromatin spreading downstream of the silent mating-type locus HMR. Belongs to the MYST (SAS/MOZ) family.