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 trimethylated lysine residues in histones, and possibly also other proteins. Regulator of cellular lifespan by maintaining the repression of CDKN2A, but not by inducing telomerase activity. Component of a PRC1-like complex. Interacts with RING1 and RNF2/RING1B, but not with BMI1, EED or EZH2. Interacts with PCGF1, PCGF2, PCGF3, PCGF5 and PCGF6. The human orthologuous proteins of Drosophila Polycomb group protein Pc, CBX2, CBX4, CBX6, CBX7 and CBX8, show distinct nuclear localizations, contribute differently to transcriptional repression, and appear to be part of distinct PRC1-like protein complexes.