The enzymes responsible for the reversible acetylation/ deacetylation process of histones are histone acetyltransferases (HATs) and histone deacetylases (HDACs), respectively. HATs act as transcriptional coactivators and HDACs are part of transcriptional corepressor complexes. Mammalian HDACs can be divided into three classes according to sequence homology. Class I consists of the yeast Rpd3 like proteins HDAC1, HDAC2, HDAC3, and HDAC8. Class II consists of the yeast Hda1 like proteins HDAC1