HATs are divided into three main families, GNAT (Gcn5-related N-acetyltransferase), MYST (MOZ/Ybf2/Sas2,3/Tip60), and CBP/p300 (CREB-binding protein/protein acetyltransferase of 300 kD). The most prominent members of the GNAT family are GCN5 and PCAF (p300/CBP-Associated Factor), both of which acetylate histone H3 and H4. While both enzymes are expressed ubiquitously, levels of GCN5 are highest in brain and testes, and levels of PCAF are highest in liver [31]. The MYST family of HATs is related by sequence similarity but has many diverse functions, from regulating HIV gene expression (Tip60) to leukemia (MOZ, MORF). Most MYST HATs have been shown to acetylate histone H3, H4, and H2A. The CBP/p300 family of HATs is the best studied in brain and has been implicated in learning and memory and drug addiction [32–35]. Mutations in CBP cause Rubinstein–Taybi Syndrome, an autosomal dominant condition characterized by mental retardation and other abnormalities [20]. CBP and p300 are distinct proteins but often referred to interchangeably due to their high degree of similarity. CBP/p300 can acetylate H2A, H2B, H3, and H4 and are recruited to specific genes through their interactions
