Transcriptional repressor. Binds specifically to the DNA sequence 5'-GACTNGACT-3'. Has tumor suppressor activity. May play a role in control of cell proliferation and/or neural cell development. Regulates proliferation of early T progenitor cells by maintaining expression of HES1. Also plays a role in antero-posterior specification of the axial skeleton and negative regulation of the self-renewal activity of hematopoietic stem cells (By similarity). Component of a Polycomb group (PcG) multiprotein PRC1-like complex, a complex class required to maintain the transcriptionally repressive state of many genes, including Hox genes, throughout development. PcG PRC1 complex acts via chromatin remodeling and modification of histones; it mediates monoubiquitination of histone H2A 'Lys-119', rendering chromatin heritably changed in its expressibility (PubMed:26151332). Within the PRC1-like complex, regulates RNF2 ubiquitin ligase activity (PubMed:26151332). Exists as both a monomer and homodimer (By similarity). Component of a PRC1-like complex (PubMed:19636380, PubMed:21282530, PubMed:26151332). Interacts with CBX8, RING1 AND RNF2 (PubMed:19636380). Interacts with CBX7 (By similarity). Interacts with PHC2 (By similarity). Detected in all tissues examined with high expression found in placenta lung and kidney and low expression, in liver, pancreas and skeletal muscle. Phosphorylated. Homodimer formation is regulated by phosphorylation with only unphosphorylated proteins forming homodimers. The disease is caused by variants affecting the gene represented in this entry.