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. In the PRC1 complex, it is required to stimulate the E3 ubiquitin-protein ligase activity of rnf2. Component of a PRC1-like complex (By similarity). Homodimer. Interacts with cbx2. Maternally derived transcript is detected at high levels at 1 and 3 hours post-fertilization (hpf). Not detectable at 6 and 9 hpf. Detected at intermediate levels at 12 and 15 hpf. Highly expressed at 18 and 24 hpf, after which expression decreases again. Detected in the anterior embryo at the 6 somites stage. Detected in hindbrain, rhombomeres and telencephalon at the 18 somites stage. Restricted to the anterior embryo, including brain, otic vesicles, and optic stalks in 24 hpf embryo. Detected in pectoral fin buds in 48 hpf embryo.