Histone acetyltransferases (HATs) are a diverse group of enzymes catalyzing a posttranslational modification of acetylation in which the acetyl group from the acetyl-CoA cofactor is transferred to the Nζ nitrogen of the target lysine side chain within histones. Based on the sequence divergence within the HAT domain, HATs is classified into at least five distinct families, including HAT1 family, Gcn5/PCAF family, MYST family, p300/CBP family and Rtt109 family. Despite the sequence divergence, a structurally conserved core region has been identified within each of the protein families, which contains a three-stranded β-sheet with a α—helix corresponding to the A and D regions of the Gcn5-related N-acetyltransferases (GNAT) proteins.