Histone deacetylase (HDAC) proteins are involved in histone deacetylation, or the removal of an acetyl group to lysine residues in the N-terminal tail and on the surface of the nucelosome core of histone proteins. They play a role in adjusting chromatin structure, leading to increased or decreased gene transcription levels. In general, histone deacetylation is linked to transcriptional repression.