HDAC 3 is a member of the class I mammalian histone deacetylase family, which plays an important role in modulating the eukaryotic chromatin structure. Human HDAC 3 is composed of 428 amino acid residues. HDAC 3 interacts with a growing number of transcriptional factors including SMRT and N-CoR. The interacting complexes bind to specific regions of chromatin and regulate gene transcription in these regions.