From loops to chains: unraveling the mysteries of polyubiquitin chain specificity and processivity.

Regulated protein degradation via polyubiquitination controls almost every aspect of eukaryotic cellular biology; however, the precise mechanism by which specifically linked polyubiquitin chains are formed on target proteins as well as how the processivity of chain elongation is achieved remains a mystery. Recent work using the yeast ubiquitin ligase SCF(Cdc4) and the ubiquitin conjugating enzyme, Cdc34, has helped to answer these questions by identifying the determinants of lysine-48 specific ubiquitin chain polymerization.