Histone deacetylase that catalyzes 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. Also functions as deacetylase for non-histone targets, such as NR1D2, RELA, SP1, SP3 and TSHZ3. 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 (By similarity). 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 (By similarity). In addition to protein deacetylase activity, also has protein-lysine deacylase activity: acts as a protein decrotonylase by mediating decrotonylation ((2E)-butenoyl) of histones (By similarity). H2O + N(6)-acetyl-L-lysyl-[histone] = acetate + L-lysyl-[histone] H2O + N(6)-acetyl-L-lysyl-[protein] = acetate + L-lysyl-[protein] H2O + N(6)-(2E)-butenoyl-L-lysyl-[protein] = (2E)-2-butenoate + L-lysyl-[protein] Part of the core histone deacetylase (HDAC) complex composed of HDAC1, HDAC2, RBBP4 and RBBP7. The core complex associates with MTA2, MBD2, MBD3, MTA1L1, CHD3 and CHD4 to form the nucleosome remodeling and histone deacetylation (NuRD) complex, or with SIN3, SAP18 and SAP30 to form the SIN3 HDAC complex. Component of a BHC histone deacetylase complex that contains HDAC1, HDAC2, HMG20B/BRAF35, KDM1A, RCOR1/CoREST and PHF21A/BHC80. The BHC complex may also contain ZMYM2, ZNF217, ZMYM3, GSE1 and GTF2I. Component of a mSin3A corepressor complex that contains SIN3A, SAP130, SUDS3/SAP45, ARID4B/SAP180, HDAC1 and HDAC2. Found in a trimeric complex with APBB1 and TSHZ3; the interaction between HDAC1 and APBB1 is mediated by TSHZ3. Component of a RCOR/GFI/KDM1A/HDAC complex. Part of a complex composed of TRIM28, HDAC1, HDAC2 and EHMT2. Part of a complex containing at least CDYL, MIER1, MIER2, HDAC1 and HDAC2. The large PER complex involved in the histone deacetylation is composed of at least HDAC1, PER2, SFPQ and SIN3A. Associates with the 9-1-1 complex; interacts with HUS1. Found in a complex with DNMT3A and HDAC7. Interacts with the non-histone region of MACROH2A1. Interacts with TRIM28; the interaction recruits HDAC1 to E2F1 and inhibits its acetylation. Interacts with SP1; the interaction deacetylates SP1 and regulates its transcriptional activity. Interacts with SP3; the interaction deacetylates SP3 and regulates its transcriptional activity. In vitro, C(18) ceramides increase this interaction and the subsequent SP3 deacetylation and SP3-mediated repression of the TERT promoter. Interacts with TSHZ3 (via N-terminus); the interaction is direct. Interacts with APEX1; the interaction is not dependent on the acetylated status of APEX1. Interacts with C10orf90/FATS (via its N-terminal); the interaction prevents binding of HDAC1 to CDKN1A/p21 and facilitates the acetylation and stabilization of CDKN1A/p21. Interacts with CDKN1A/p21. Interacts with CDK5 complexed to CDK5R1 (p25). Interacts directly with GFI1 and GFI1B. Interacts with NR1D2 (via C-terminus). Interacts with TSC22D3 isoform 1; this interaction affects HDAC1 activity on MYOG promoter and thus inhibits MYOD1 transcriptional activity. Interacts with BAZ2A/TIP5, BANP, BCL6, BCOR, BHLHE40/DEC1, BRMS1, BRMS1L, CBFA2T3, CHFR, CIART, CRY1, DAXX, DDIT3/CHOP, DDX5, DNMT1, E4F1, EP300, HCFC1, HDAC9, INSM1, NFE4, NR4A2/NURR1, MIER1, KDM4A, KDM5B, KLF1, MINT, NRIP1, PCAF, PHB2, PRDM6, PRDM16, RB1, RERE, SAMSN1, SAP30L, SETDB1, SMAD3, SMARCA4/BRG1, SMYD2, SUV39H1, TGIF, TGIF2, TRAF6, UHRF1, UHRF2, ZMYND15, ZNF431 and ZNF541. Interacts with KDM5A; this interaction impairs histone deacetylation (By similarity). Interacts with DNTTIP1. Identified in a histone deacetylase complex that contains DNTTIP1, HDAC1 and MIDEAS; this complex assembles into a tetramer that contains four copies of each protein chain. Interacts with CCAR2. Interacts with PPHLN1. Found in a complex with YY1, SIN3A and GON4L. Interacts with CHD4. Found in a complex composed of at least SINHCAF, SIN3A, HDAC1, SAP30, RBBP4, OGT and TET1. Interacts with SIN3A. Interacts with DHX36; this interaction occurs in a RNA-dependent manner (By similarity). Interacts with ZBTB7A (By similarity). Interacts with SMAD4; positively regulated by ZBTB7A (By similarity). Interacts with PACS2 (By similarity). Forms a complex comprising APPL1, RUVBL2, APPL2, CTNNB1 and HDAC2 (By similarity). Interacts with ZNF638 (By similarity). Interacts with SPHK2 (By similarity). Interacts with ERCC6 (By similarity). Interacts with NSD2 (By similarity). Interacts with SMYD4 (via MYND-type zinc finger) (By similarity). Interacts with PWWP2A in a MTA1-dependent manner (By similarity). Interacts with PWWP2B (By similarity). Interacts with ZNF516 and BRCC3; these interactions are enhanced in the presence of PWWP2B (By similarity). Interacts with SANBR (via the BTB domain) (By similarity). Sumoylated on Lys-444 and Lys-476; which promotes enzymatic activity. Desumoylated by SENP1. Phosphorylation on Ser-421 and Ser-423 promotes enzymatic activity and interactions with NuRD and SIN3 complexes. Phosphorylated by CDK5. Ubiquitinated by CHFR and KCTD11, leading to its degradation by the proteasome. Belongs to the histone deacetylase family. HD type 1 subfamily.