Histone acetylation is regulated mainly by the opposing activities of two families of enzymes—the HATs that acetylate histones and the HDACs (Shahbazian and Grunstein 2007). HATs, which transfer acetyl groups from acetyl-CoA to lysine residues, include three main subfamilies that are functionally distinct—GCN5-related N-acetyltransferase (GNAT), MYST histone acetyltransferase, and p300/CBP. HDACs, in contrast, remove acetyl groups from histones; they comprise four groups (classes I–IV) (Zhang and Dent 2005), some of which are dependent on Zn2+ (Haberland et al. 2009). Class III HDACs, known as sirtuins, however, require NAD+ as a cofactor. In general, histone acetylation results in transcriptional activation, whereas deacetylation is associated with gene silencing (Lane and Chabner 2009).
