SIC1 is ubiquitinated in vitro by a pathway that requires CDC4, CDC34, and cyclin/CDK activities.

摘要: Traversal from G1 to S-phase in cycling cells of budding yeast is dependent on the destruction cyclin/CDK inhibitor SIC1. Genetic data suggest that SIC1 proteolysis mediated by ubiquitin pathway and requires action CDC34, CDC4, CDC53, SKP1, CLN/CDC28. As a first step defining functions corresponding gene products, we have reconstituted multiubiquitination DEAE-fractionated extract. Multiubiquitination depends cyclin/CDC28 protein kinase CDC34 ubiquitin-conjugating enzyme. Ubiquitin chain formation abrogated cdc4ts mutant extracts assembly restored addition exogenous suggesting direct role for this multiubiquitination. Deletion analysis indicates N-terminal 160 residues are both necessary sufficient serve as substrate CDC34-dependent ubiquitination. The complementary C-terminal segment binds cyclin CLB5, indicating modular structure