A complex of Cdc4p, Skp1p, and Cdc53p/cullin catalyzes ubiquitination of the phosphorylated CDK inhibitor Sic1p.
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 SCFCdc4p. When mixed together, SCFCdc4p 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.
Feldman
R M
RM
Division of Biology, California Institute of Technology, Pasadena 91125, USA.
Correll
C C
CC
Kaplan
K B
KB
Deshaies
R J
RJ
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D044842:Cullin Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D004791:Enzyme Inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D044783:F-Box Proteins; D005656:Fungal Proteins / Q000302:isolation & purification / Q000378:metabolism*; D007313:Insecta; D010766:Phosphorylation; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*
C080443:CDC4 protein, S cerevisiae; C100988:Cdc53 protein, S cerevisiae; D018797:Cell Cycle Proteins; D044842:Cullin Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D004791:Enzyme Inhibitors; D044783:F-Box Proteins; D005656:Fungal Proteins; D016271:Proto-Oncogene Proteins c-myc; D011994:Recombinant Proteins; D044786:S-Phase Kinase-Associated Proteins; C086926:SIC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014452:Ubiquitins; D044767:Ubiquitin-Protein Ligases