E3 SUMO-protein ligase which facilitates SUMO1 conjugation by UBE2I (PubMed:12679040). Involved in the sumoylation of HNRNPK, a p53/TP53 transcriptional coactivator, hence indirectly regulates p53/TP53 transcriptional activation resulting in p21/CDKN1A expression. Monosumoylates ZNF131 (PubMed:22825850). 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:12167701, PubMed:19636380, 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 (PubMed:12167701, PubMed:19636380, PubMed:21282530). Binds to histone H3 trimethylated at 'Lys-9' (H3K9me3) (By similarity). Plays a role in the lineage differentiation of the germ layers in embryonic development (By similarity). Protein modification; protein sumoylation. Interacts with histone H3-K9Me3 (By similarity). Interacts with CHTOP (By similarity). Component of a PRC1-like complex (PubMed:12167701, PubMed:19636380, PubMed:21282530). The composition of the PRC1 complex differs 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 (By similarity). Self-associates (PubMed:21282530). Interacts with SUV39H1 and HIPK2 (PubMed:12101246, PubMed:17018294). Interacts with CSNK2B (PubMed:21282530). May interact with H3C15, H3C1 and RNF2 (PubMed:18927235). Interacts with SUMO1P1/SUMO5 (PubMed:27211601). Interacts with PRDM1/Blimp-1 (PubMed:28842558). Localization to nuclear polycomb bodies is required for ZNF131 sumoylation (PubMed:22467880). Localized in distinct foci on chromatin (PubMed:18927235). Ubiquitous. The polyhistidine repeat may act as a targeting signal to nuclear speckles. Phosphorylated on Thr-497 by HIPK2 upon DNA damage. This phosphorylation stimulates E3 SUMO-protein ligase activity and promotes sumoylation on Lys-494, as well as sumoylation of other target proteins, such as HNRNPK. The human orthologs of the Drosophila Polycomb group protein Pc are CBX2, CBX4, CBX6, CBX7 and CBX8. These show distinct nuclear localizations, contribute differently to transcriptional repression, and appear to be part of distinct PRC1-like protein complexes. The hPRC-H complex purified in PubMed:12167701 probably presents a mixture of different complexes containing different Polycomb group proteins. Aberrant splicing.