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. The complex composed of RNF2, UB2D3 and BMI1 binds nucleosomes, and has activity only with nucleosomal histone H2A. In the PRC1-like complex, regulates the E3 ubiquitin-protein ligase activity of RNF2/RING2. Component of a PRC1-like complex. Identified in a PRC1-like HPRC-H complex with CBX2, CBX4, CBX8, PHC1, PHC2, PHC3 RING1 and RNF2. Interacts with RNF2/RING2 (By similarity). Interacts with RING1 (By similarity). Part of a complex that contains RNF2, UB2D3 and BMI1, where RNF2 and BMI1 form a tight heterodimer, and UB2D3 interacts only with RNF2. The complex composed of RNF2, UB2D3 and BMI1 binds nucleosomes, and has activity only with nucleosomal histone H2A. Interacts with CBX7 and CBX8. Interacts with SPOP. Part of a complex consisting of BMI1, CUL3 and SPOP. Interacts with E4F1. Interacts with PHC2 (By similarity). Interacts with zinc finger protein ZNF277 (By similarity). May be part of a complex including at least ZNF277, BMI1 and RNF2/RING2 (By similarity). Transcripts are found in thymic lymphomas bearing insertions of the gene. Transcription is low or undetectable in mid-gestational fetal liver, neonatal and adult spleen, and in healthy lymph nodes. Down-regulated by oxidative stress. May be polyubiquitinated; which does not lead to proteasomal degradation. Monoubiquitinated.