RING fingers mediate ubiquitin-conjugating enzyme (E2)-dependent ubiquitination

A RING finger-containing protein (AO7) that binds ubiquitin-conjugating enz ymes (E2s) and is a substrate for E2-dependent ubiquitination was identifie d. Mutations of cation-coordinating residues within AO7's RING finger aboli shed ubiquitination,as did chelation of zinc. Several otherwise-unrelated R ING finger proteins, including BRCA1, Siah-1, TRC8, NF-X1, kf-1, and Praja1 , were assessed for their ability to facilitate E2-dependent ubiquitination , In all cases, ubiquitination was observed. The RING fingers were implicat ed directly in this activity through mutations of metal-coordinating residu es or chelation of zinc. These findings suggest that a large number of RING finger-containing proteins, with otherwise diverse structures and function s, may play previously unappreciated roles in modulating protein levels via ubiquitination.