E3 SUMO-protein ligase which facilitates SUMO1 conjugation by UBE2I. Involved in the sumoylation of HNRNPK, a p53/TP53 transcriptional coactivator, hence indirectly regulates p53/TP53 transcriptional activation resulting in p21/CDKN1A expression. 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 (By similarity). 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 (By similarity). Binds to histone H3 trimethylated at 'Lys-9' (H3K9me3) (PubMed:16537902). Plays a role in the lineage differentiation of the germ layers in embryonic development (PubMed:22226355). Protein modification; protein sumoylation. Interacts with SUV39H1 and HIPK2 (By similarity). Interacts with CSNK2B (By similarity). Component of a PRC1-like complex (By similarity). 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 (PubMed:22226355). Interacts with RNF2 (PubMed:22226355). Interacts (via chromodomain) with histone H3K9Me3 and single-stranded RNA (ssRNA) (PubMed:16537902). Interacts with CHTOP (PubMed:22872859). May interact with H3C15 and H3C1 (By similarity). Interacts with PRDM1 (By similarity). Expressed in embryoid bodies. The polyhistidine repeat may act as a targeting signal to nuclear speckles.