Vincent Allfrey and his colleagues first identified lysine acetylation on histones in 1964. Acetylation is an evolutionarily conserved post-translational modification (PTM) that is present in both prokaryotes and eukaryotes. Histone acetylation and deacetylation are catalyzed by histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. HAT and HDAC-catalyzed acetylation play an important role in the regulation of eukaryotic gene expression. These two kinds of enzymes regulate the acetylation level of core histones through reversible modification of core histone, thus regulating the initiation and elongation of transcription. In general, histone acetylation promotes transcription, while deacetylation inhibits transcription.