Chromatin is a highly specialized structure composed of tightly compacted chromosomal DNA. Gene expression within the nucleus is controlled, in part, by a host of protein complexes which continuously pack and unpack the chromosomal DNA. One of the known mechanisms of this packing and unpacking process involves the acetylation and deacetylation of the histone proteins comprising the nucleosomal core. Acetylated histone proteins confer accessibility of the DNA template to the transcriptional machinery for expression. Histone deacetylases (HDACs) are chromatin remodeling factors that deacetylate histone proteins and thus, may act as transcriptional repressors. HDACs are classified by their sequence homology to the yeast HDACs and there are currently 2 classes. Class I proteins are related to Rpd3 and members of class II resemble Hda1p.
