posted 12-06-2012 01:52 AM            

Histones are the chief protein components of chromatin. They act as spools around which DNA winds. Covalent modification of histone proteins through acetylation and deacetylation affects chromatin structure and regulates gene expression. Histone hyperacetylation is well correlated with increased transcription, whereas hypoacetylation correlates with transcriptional repression. Histone deacetylases (HDACs), which catalyze the removal of acetyl groups from a å-N-acetyl lysine amino acid on a histone, act as transcriptional repressors of genes. Histone deacetylases have been grouped into three classes. Class I (HDAC 1, 2, 3, 8) and Class II (HDAC4, 5, 6, 7, and 9) are zinc-containing hydrolase’s enzymes. The third class of deacetylases consists of the members of the sirtuin family of enzymes (Sirt 1 to 7). Inhibitors of HDAC classes I and II are being studied as a treatment for cancer and neurodegenerative diseases such as Huntington’s and Alzheimer’s diseases. The Sirtuin 1 (class III) enzyme represents a target for treatment of age-related diseases and type II diabetes.

Histone acetyltransferases (HATs) enzymes regulate the acetylation of histones and non-histone proteins. The acetylation of the å-amino groups of lysine residues present at histone tails not only correlates largely with transcriptional activation, but is also involved in DNA replication, DNA repair and protein–protein interactions.