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 (PubMed:21282530). 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 (PubMed:18927235). Recruitment to chromatin might occur in an H3K27me3- independent fashion (By similarity). May have a PRC1-independent function in embryonic stem cells (By similarity). {ECO:0000250|UniProtKB:Q9DBY5, ECO:0000269|PubMed:18927235, ECO:0000269|PubMed:21282530}. This is the function of CBX6 (chromobox 6, ENSG00000183741).