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. Component of a PRC1-like complex. Interacts with CBX4 (By similarity). Interacts with BMI1, PCGF2, PHC1 and RNF2 (PubMed:9627119, PubMed:16024804, PubMed:27827373). Interacts with CHTOP (PubMed:22872859). Interacts with the N-terminal region of the SP1 transcription factor and with MAPKAPK2 (By similarity). Isoform 2 is ubiquitously expressed in embryos and adult tissues at much higher level than isoform 1. Detected at 11.5 dpc in the developing brain, in the ventricular zones of the cortex and ganglionic eminences as well as in adult, in mature structures such as the granule cell layer of the dentate gyrus and cerebellum. HD1 motif interacts with SAM domain of PHC1. Mice are viable and fertile but show posterior transformations of the axial skeleton and premature senescence of mouse embryonic fibroblast associated with derepression of Hox cluster genes and Cdkn2a genes, respectively. Mice lacking Phc2 and Phc1 die at an early gestational stage. Mice mutant for Phc1 and/or Phc2 demonstrate that Phc1 and Phc2 mutations affect synergistically the survival of embryos in a gene dosage-dependent manner and thus show functional redundancy of Phc1 and Phc2.