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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.

Pubmed ID: 9346239


  • Feldman RM
  • Correll CC
  • Kaplan KB
  • Deshaies RJ



Publication Data

October 17, 1997

Associated Grants

  • Agency: NIGMS NIH HHS, Id: R01 GM52466-01

Mesh Terms

  • Animals
  • Cell Cycle Proteins
  • Cullin Proteins
  • Cyclin-Dependent Kinase Inhibitor Proteins
  • Enzyme Inhibitors
  • F-Box Proteins
  • Fungal Proteins
  • Insects
  • Phosphorylation
  • Proto-Oncogene Proteins c-myc
  • Recombinant Proteins
  • S-Phase Kinase-Associated Proteins
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Ubiquitin-Protein Ligases
  • Ubiquitins