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. Promotes histone H3 trimethylation at 'Lys-9' (H3K9me3). Binds to histone H3 trimethylated 'Lys-9' (H3K9me3) or at 'Lys-27' (H3K27me3). May possibly also bind trimethylated lysine residues in other proteins (in vitro). Binds non-coding, single-stranded and double-stranded RNA. Plays a role in the timely repression of differentiation-specific genes in pluripotent embryonic stem cells to maintain the undifferentiated state. Regulator of cellular lifespan by maintaining the repression of CDKN2A, but not by inducing telomerase activity (By similarity). 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). The composition of the PRC1 complex may differ between the PRC1 complex in pluripotent embryonic stem cells containing RNF2, CBX7 and PCGF2, and the PRC1 complex in differentiating cells containing RNF2, CBX2, CBX4 and BMI1. Interacts with RING1. Interacts with RNF2/RING1B. Interacts with PCGF1, PCGF2, PCGF3, PCGF5 and PCGF6. Interacts (via chromodomain) with histone H3K9Me3 and H3K27me3. Interacts with H3K9Me2 and H4K20Me1. Interacts (via chromodomain) with single-stranded and double-stranded RNA; RNA binding seems to be required for the localization to chromatin (By similarity). Requires trimethylation at 'Lys-27' (H3K27me3) for the localization to chromatin. Localizes to facultative heterochromatin and to the inactivated X chromosome in females.