Polycomb group RING finger (PGRF) proteins are RING-RAWUL domain-containing proteins found in a variety of complexes that mediate post-translational protein modification. The best characterised of these are the Polycomb group complexes, epigenetic regulators that promote the formation of heterochromatin. Other ubiquitin-ligase PGRF complexes, such as the Siesta-RING1 complexes may function outside of canonical Polycomb repression. (Adapted from FBrf0264828.)