UBC3 Antibody #4997

Ubiquitin can be covalently linked to many cellular proteins by the ubiquitination process, which targets proteins for degradation by the 26S proteasome. Three components are involved in the target protein-ubiquitin conjugation process. Ubiquitin is first activated by forming a thiolester complex with the activation component E1; the activated ubiquitin is subsequently transferred to the ubiquitin-carrier protein E2, and then from E2 to ubiquitin ligase E3 for final delivery to the epsilon-NH2 of the target protein lysine residue (1-3). Combinatorial interactions of different E2 and E3 proteins result in substrate specificity (4). Recent data suggest that activated E2 associates transiently with E3, and that the dissociation is a critical step for ubiqitination (5). UBC3, the mammalian orthologue of yeast Cdc34, and UBC3B, a UBC3 family member, are E2 ubiquitin-carrier proteins. These proteins contain a conserved core domain containing a cysteine residue, which forms the thioester bond with ubiquitin (6). UBC3 in concert with the SCFSkp2 (Skp1, Cullin and F-box protein/Skp2) complex mediates cell cycle progression from G1 to S phase by targeting the CDK inhibitor p27 for proteolysis (7). UBC3B in concert with the SCFb-Trcp (Skp1, Cullin and F-box protein/b-Trcp) complex mediates degradation of b-catenin (6).