Seems to be involved in transcriptional silencing in heterochromatin-like complexes (By similarity). Involved in epigenetic repression (By similarity). Probably does not act as global transcriptional repressor (PubMed:23028351). Plays a role in linking epigenetic regulation with the innate immune response (PubMed:22083954). Acting in concert with chromobox protein homolog hpl-2 and histone H1 protein his-24, involved in reproduction, somatic gonad development, male tail development and vulval cell fate decisions; perhaps as a result of modulating expression of Hox genes mab-5 and egl-5 (PubMed:23028351, PubMed:16905130). Role in growth and somatic gonad development is antagonized by histone-lysine N-methyltransferase set-2/SET1 (PubMed:17967446). Required for larval development, acting redundantly with hpl-2 (PubMed:26476455, PubMed:16905130). Plays a role in the formation of the vulva and in fertility, acting together with a CoREST-like complex, and hpl-2 (PubMed:26476455, PubMed:16905130). Interacts with histone demethylase spr-5 (PubMed:26476455). Interacts with chromobox protein homolog hpl-2 (PubMed:26476455, PubMed:22083954). Interacts with histone H3 tails methylated at 'Lys-9' (H3K9me3) and 'Lys-23'(H3K23me2) (PubMed:26476455). Interacts with histone H1 variant his-24 (when monomethylated at 'Lys-14'); the interaction is direct (PubMed:22083954). May interact with the REST corepressor rcor-1, histone deacetylase hda-1, and the histone demethylase lsd-1 (PubMed:26476455). Partially co-localizes with histone H3 tails methylated at 'Lys-9' (H3K9me3) and 'Lys-23'(H3K23me2) in chromatin (PubMed:26476455). Localizes to distinct nuclear foci, not overlapping significantly with hpl-2, in embryonic cells (PubMed:26476455, PubMed:16905130). Expressed in embryos at about the 50 cell stage (PubMed:16905130). Expressed in most, but not all cells of larvae and adults, especially in neuronal and hypodermal cells (PubMed:16905130). RNAi-mediated knockdown in a hpl-2 mutant background causes larval arrest.