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 (By similarity). Within the PRC1-like complex, regulates RNF2 ubiquitin ligase activity (By similarity). Plays a redundant role with PCGF3 as part 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 (By similarity). Component of a PRC1-like complex that contains PCGF5, RNF2 and UBE2D3. Interacts with RNF2; the interaction is direct. Interacts with CBX6, CBX7 and CBX8. Interacts with AUTS2; the interaction is direct. Identified in a complex that contains AUTS2, PCGF5, CSNK2B and RNF2. Recruited by the non-coding RNA Xist to specific nuclear foci that probably correspond to the inactivated X chromosome.