A Complex of Cdc4p, Skp1p, and Cdc53p/Cullin Catalyzes Ubiquitination of the Phosphorylated CDK Inhibitor Sic1p

• Published in: Cell 1997-10, Vol.91 (2), p.221-230
• Main Authors: Feldman, R.M.Renny, Correll, Craig C, Kaplan, Kenneth B, Deshaies, Raymond J
• Format: Article
• Language: English
• Subjects: Animals; Cell Cycle Proteins - genetics; Cell Cycle Proteins - isolation & purification; Cell Cycle Proteins - metabolism; Cullin Proteins; Cyclin-Dependent Kinase Inhibitor Proteins; Enzyme Inhibitors - isolation & purification; Enzyme Inhibitors - metabolism; F-Box Proteins; Fungal Proteins - isolation & purification; Fungal Proteins - metabolism; Insecta; Phosphorylation; Proto-Oncogene Proteins c-myc - genetics; Proto-Oncogene Proteins c-myc - metabolism; Recombinant Proteins - metabolism; S-Phase Kinase-Associated Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Ubiquitin-Protein Ligases; Ubiquitins - metabolism
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/S0092-8674(00)80404-3

In S. cerevisiae, the G1/S transition requires Cdc4p, Cdc34p, Cdc53p, Skp1p, and the Cln/Cdc28p cyclin-dependent kinase (Cdk). These proteins are thought to promote the proteolytic inactivation of the S-phase Cdk inhibitor Sic1p. We show here that Cdc4p, Cdc53p, and Skp1p assemble into a ubiquitin ligase complex named SCF Cdc4p. When mixed together, SCF Cdc4p subunits, E1 enzyme, the E2 enzyme Cdc34p, and ubiquitin are sufficient to reconstitute ubiquitination of Cdk-phosphorylated Sic1p. Phosphorylated Sic1p substrate is specifically targeted for ubiquitination by binding to a Cdc4p/Skp1p subcomplex. Taken together, these data illuminate the molecular basis for the G1/S transition in budding yeast and suggest a general mechanism for phosphorylation-targeted ubiquitination in eukaryotes.