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-like 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:22325148, PubMed:28596365). Component of a PRC1-like complex that mediates monoubiquitination of histone H2A 'Lys-119' on the X chromosome and is required for normal silencing of one copy of the X chromosome in XX females (PubMed:28596365). May stimulate ubiquitination of histone H2A 'Lys-119' by recruiting the complex to target sites (PubMed:22325148, PubMed:28596365). Inhibits ubiquitination and subsequent degradation of TP53, and thereby plays a role in regulating transcription of TP53 target genes (By similarity). May also regulate the ubiquitin-mediated proteasomal degradation of other proteins like FANK1 to regulate apoptosis (PubMed:17874297). May be implicated in the regulation of the transcription as a repressor of the transcriptional activity of E4TF1 (By similarity). May bind to DNA (PubMed:19170609). May play a role in the repression of tumor growth and metastasis in breast cancer by down-regulating SRRM3 (PubMed:27748911). Monomer. Component of repressive BCOR complex containing Polycomb group subcomplex at least composed of BCOR, PCGF1, RING1 and RNF2/RING2 (By similarity). Component of PCR1-like complexes (PubMed:22325148, PubMed:28596365). Interacts with PCGF1. Part of a PCR1-like complex that contains AUTS2, PCGF5, RNF2, CSNK2B AND RYBP. Interacts with RNF2; the interaction is direct (By similarity). Interacts with CBX2, YAF2, RING1 and RNF2 (PubMed:10369680, PubMed:19170609, PubMed:22226355). Interacts with ubiquitin and ubiquitinated proteins (PubMed:17070805). Interacts with ubiquitinated histone H2A (PubMed:17070805). Interacts with apoptin, DEDD, FADD, CASP8, CASP10, YY1 and GABPB1. Together with GABPB1 and YY1, it forms a ternary complex, probably being the bridge factor between these two transcription factors. Interacts with MDM2, and thereby inhibits ubiquitination of TP53. Identified in a ternary complex containing MDM2, TP53 and RYBP. Interacts with FANK1; may prevent the ubiquitin-mediated proteasomal degradation of FANK1 (By similarity). Interacts with IFT57 (PubMed:17874297). Primarily found in the nucleus. Detected in a punctate pattern likely to represent Polycomb group (PcG) bodies. Expressed in embryonic stem cells. At 9.0 dpc, selectively expressed in cells of the developing nervous system and from day E.5 onwards, expressed ubiquitously. Intrinsically unstructured in the absence of binding partners. Folds upon binding to DNA or RNF2. Monoubiquitinated. Embryonically lethal. Embryos die at early postimplantation stage.