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 (By similarity). Component of a PRC1-like complex (PubMed:16359901). Interacts with RING1, RNF2, PCGF1, PCGF2, PCGF3, BMI1, PCGF5, PCGF6 and PHC2 (PubMed:16359901). Interacts with histone H3 (By similarity). Interacts with MLLT3 (Ref.8). Interacts with PHC2 (By similarity). Interacts (via chromodomain) with single-stranded RNA (PubMed:16537902). Localizes to the inactivated X chromosome in females.