The protein encoded by this gene is a member of the tripartite motif (TRIM) family. The TRIM motif includes three zinc-binding domains, a RING, a B-box type 1 and a B-box type 2, and a coiled-coil region. This protein is part of the RoSSA ribonucleoprotein which includes a single polypeptide and one of four small RNA molecules. The RoSSA particle localizes to both the cytoplasm and the nucleus. RoSSA interacts with autoantigens in patients with Sjogren syndrome and systemic lupus erythematosus. The function of the RoSSA particle has not been determined. Two alternatively spliced transcript variants for this gene have been described, however, the full length nature of one variant has not been determined.Synonyms: E3 ubiquitin-protein ligase TRIM21, RING finger protein 81, RNF81, Ro(SS-A), SSA1, Sjoegren syndrome type A antigen, TRIM21, Tripartite motif-containing protein 21