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). Component of a PRC1-like complex. Isoform 1 expression is stronger at the posterior border than in the anterior region within individual somites; On the contrary, isoform 2 expression is higher at the posterior border. Isoform 1 is expressed during the segmentation period and is initially detected at the 7-8 somite stage; Isoform 2 is expressed at all developmental stages and appears in the first somites.