RING1 (ring finger protein 1) is an E3 ubiquitin ligase component of the polycomb repressive complex 1 (PRC1) that primarily functions in epigenetic chr6 regulation 1. While RING1 contributes to H2A lysine 119 monoubiquitination (H2AK119ub1) within PRC1, it serves a modulatory role compared to RNF2, which carries the main catalytic activity 1. RING1 mediates K48-linked ubiquitination of diverse substrates beyond histones, including p53 and GSDMD. In pancreatic cancer, RING1-mediated p53 ubiquitination promotes gemcitabine resistance by enhancing pyrimidine biosynthesis 2. In innate immunity, RING1 negatively regulates pyroptosis by ubiquitinating GSDMD, with RING1 loss increasing susceptibility to bacterial infections (S. typhimurium, M. tuberculosis) and exacerbating sepsis 3. During neurogenesis, RING1 contributes broadly to H2AK119ub1 placement, and its hypomorphic variants impair DNA damage repair in neural progenitor cells without substantially affecting gene expression 1. Clinically, RING1 upregulation associates with poor prognosis in hepatocellular carcinoma, correlating with tumor aggression and Ki-67 proliferation markers 4. RING1 thus functions as a multifaceted ubiquitin ligase regulating both chr6-dependent processes and substrate-specific ubiquitination in cancer and immune responses.