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. Possibly contributes to the target selectivity of the PRC1 complex by binding specific regions of chromatin (By similarity). Recruitment to chromatin might occur in an H3K27me3-independent fashion (PubMed:22226355, PubMed:16537902). May have a PRC1-independent function in embryonic stem cells (PubMed:22226355). Component of a PRC1-like complex. Distinct PRC1-like core complexes are composed of a RING1 subunit (RING1B or RING1A), one of the six PCGF proteins (PCGF1-6), one PHC protein (PHC1-3) and one of the CBX proteins (CBX2, CBX4, CBX6, CBX7 or CBX8). Interacts with PCGF1, PCGF2, PCGF3, BMI1, PCGF5, PCGF6, RING1 and RNF2. May interact with H3C15 and H3C1 (By similarity). Interacts (via chromodomain) with single-stranded RNA (ssRNA) (PubMed:16537902). Localizes to the inactivated X chromosome in females. Expressed in mouse embryonic stem cells.