Ring1B also known as RING2, RNF2 is a member of the RING finger family. Ring1B plays a crucial role in gene expression regulation through involvement in Polycomb group (PcG) protein complexes, which maintain silencing of developmental and cell proliferation genes. Ring1B is primarily located in the nucleus, participating in chromatin-associated class II PcG repressive complex 1 (PRC1/hPRC-H) formation. Ring1B protein is essential for Histone H2A monoubiquitination, a modification contributing to transcription repression during development. A RING-type zinc finger domain in Ring1B enables interactions with other proteins, such as Huntington interacting protein 2 (HIP2), facilitating E3 ubiquitin ligase activity. Ring1B protein is implicated in random and imprinted X chromosome inactivation in female mammals, highlighting significance in epigenetic regulation.