Transcriptional repressor (PubMed:8521824). Binds specifically to the DNA sequence 5'-GACTNGACT-3' (PubMed:8521824). Has tumor suppressor activity (PubMed:8521824). May play a role in control of cell proliferation and/or neural cell development (Probable). Regulates proliferation of early T progenitor cells by maintaining expression of HES1(PubMed:15728456). Also plays a role in antero-posterior specification of the axial skeleton and negative regulation of the self-renewal activity of hematopoietic stem cells (PubMed:8625838, PubMed:15183898). 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. Within the PRC1-like complex, regulates RNF2 ubiquitin ligase activity (By similarity). Exists as both a monomer and homodimer (PubMed:12480532). Component of a PRC1-like complex. Interacts with CBX8, RING1 AND RNF2 (By similarity). Interacts with CBX7 (PubMed:22226355). Interacts with PHC2 (PubMed:16024804). Expressed in embryonic stem cells (PubMed:22226355). Expressed in a variety of tumor cells and in neural tissues (PubMed:2246278). Developmentally regulated. Phosphorylated. Homodimer formation is regulated by phosphorylation with only unphosphorylated proteins forming homodimers. Probably related to tumorigenesis since it is expressed strongly in most tumor cell lines.