Cdc53 Background Information Cell cycle progression is controlled at a point late in G1 designated Start. Passage through Start requires the activity of the cyclin-dependent protein kinase Cdc28 (1,2). Transition from G1 to S phase requires the association of Cdc28 with members of the G1 cyclin family (3). This progression also requires the destruction of the S-phase cyclin/Cdk inhibitor, Sic1 (4). Sic1 proteolysis is mediated in part by the ubiquitin-conjugating enzyme Cdc34 (5). Cdc4, a potential ubiquitin-protein ligase, is also involved in the degradation of Sic1 (6). Another protein thought to play a role in the ubiquitin-protein ligase complex is Cdc53. This protein
binds to Cdc34 and targets phosphorylated G1 cyclins for ubiquitin-mediated degradation (7,8).
