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. Plays an important role in transcriptional regulation, cell cycle progression and developmental events (PubMed:25446273). Histone deacetylases act via the formation of large multiprotein complexes. Involved in the endoderm determination possibly by repressing end-1 expression. Also involved in vulval development, possibly by repressing lag-2 expression. Required during mitochondrial stress for the activation of genes involved in the mitochondrial unfolded protein response (mtUPR), in concert with homeobox protein dve-1 (PubMed:32934238). Promotes normal hermaphrodite (XX) development, in concert with zinc finger protein tra-4 and nasp-1, perhaps as components of a complex (PubMed:17011494). Plays a role in the regulation of longevity and mtUPR-associated innate immunity (PubMed:32934238). In association with akir-1, plays a role in regulating the transcription of antimicrobial peptide genes in response to fungal infection (PubMed:30036395). H2O + N(6)-acetyl-L-lysyl-[histone] = acetate + L-lysyl-[histone] Component of the SIN3S complex, which contains at least sin-3, hda-1, athp-1 and mrg-1 (PubMed:31602465). Probable component of a NuRD-like complex, composed of at least lin-53 and hda-1 (PubMed:17075059). Interacts with lin-53 (PubMed:9875852, PubMed:17075059). Interacts with pop-1 (PubMed:11742996). Interacts with akir-1 (PubMed:30036395). Interacts with wdr-5.1 (PubMed:31602465). Interacts with cfp-1 (PubMed:31602465). Interacts with dve-1 (PubMed:32934238). Interacts with tra-4 (PubMed:17011494). May interact with nasp-1 (PubMed:17011494). Interacts with chromobox protein homolog hpl-1. Except in the germ line where it is also cytoplasmic. Ubiquitously expressed throughout embryonic and postembryonic development. Expressed both maternally and zygotically. Sumoylated. RNAi-mediated knockdown results in embryonic lethality. RNAi-mediated knockdown results in delayed cell cycle progression (PubMed:25446273). RNAi-mediated knockdown inhibits expression of hsp-6 when adults are exposed to conditions causing mitochondrial stress (PubMed:32934238). Reduces the dve-1 protein level (PubMed:32934238). Belongs to the histone deacetylase family. HD type 1 subfamily.