Histone deacetylases: complex transducers of nuclear signals.

Histone acetylation influences both gene transcription and chromatin assembly after DNA replication and the enzymes that regulate this property of chromatin are likely to play a key role in regulating these crucial genomic functions. The steady-state level of histone acetylation is established and maintained by multiple histone acetyltransferases (HATs) and deacetylases (HDACs). Both groups of enzymes contain numerous family members, most of which have been highly conserved through evolution. The HDACs have been implicated in repression of gene expression by facilitating chromatin condensation and, like the HATs, operate as part of multi-protein complexes. The non-catalytic components of these complexes can either target the catalytic subunit to specific sites on the genome or regulate its enzymatic specificity. Kinase and phosphatase activities of intracellular signal transduction pathways may modify components of these complexes and thereby regulate their assembly, targeting or enzymatic function.