Responsible for the deacetylation of lysine residues on the N-terminal part of the core histones (H2A; H2B; H3 and H4). Histone deacetylation gives a tag for epigenetic repression and plays an important role in transcriptional regulation; cell cycle progression and developmental events. Histone deacetylases act via the formation of large multiprotein complexes. Deacetylates SP proteins; SP1 and SP3; and regulates their function. Component of the BRG1-RB1-HDAC1 complex; which negatively regulates the CREST- mediated transcription in resting neurons. Upon calcium stimulation; HDAC1 is released from the complex and CREBBP is recruited; which facilitates transcriptional activation. Deacetylates TSHZ3 and regulates its transcriptional repressor activity. Deacetylates 'Lys-310' in RELA and thereby inhibits the transcriptional activity of NF-kappa-B. Deacetylates NR1D2 and abrogates the effect of KAT5-mediated relieving of NR1D2 transcription repression activity. Component of a RCOR/GFI/KDM1A/HDAC complex that suppresses; via histone deacetylase (HDAC) recruitment; a number of genes implicated in multilineage blood cell development. Involved in CIART-mediated transcriptional repression of the circadian transcriptional activator: CLOCK-ARNTL/BMAL1 heterodimer. Required for the transcriptional repression of circadian target genes; such as PER1; mediated by the large PER complex or CRY1 through histone deacetylation. {ECO:0000269|PubMed:12837748; ECO:0000269|PubMed:16478997; ECO:0000269|PubMed:17000776; ECO:0000269|PubMed:17704056; ECO:0000269|PubMed:17996965; ECO:0000269|PubMed:19081374; ECO:0000269|PubMed:19343227}.