Histone acetylation is a dynamic process whose levels are determined by the net activities of HATs and the competing enzymes histone deacetylases (HDACs). Both activities are associated with the nuclear matrix. Six or seven different mammalian HDACs have been described. HDAC1, HDAC2 and HDAC3 are similar to yeast Rpd3 protein, while HDAC4, HDAC5 and HDAC6 are similar to yeast Hda1 protein. Histone deacetylases activities were often, but not always, associated with transcriptional repression and nucleosomal condensations. HDAC1, HDAC2 and several other HDACs are the catalytic subunits of different multiprotein regulatory complexes.
