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 HDAC10, HDAC5, HDAC6, HDAC7, HDAC9, and HDAC10. Class III comprises the yeast Sir2 like proteins. Whereas class I HDACs are ubiquitously expressed, most class II HDACs are tissue specific. HDAC10 is similar to HDAC6, both containing a unique putative second catalytic domain not found in other HDACs. However, this domain is not functional in HDAC10. The deacetylase activity of class II HDACs is regulated by subcellular localization. HDAC10 was localized to both the nucleus and cytoplasm. HDAC10 can deacetylate histones, repress transcription, and interact with HDAC3.