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Yeast Chfr homologs retard cell cycle at G1 and G2/M via Ubc4 and Ubc13/Mms2-dependent ubiquitination.

Checkpoint with forkhead-associated and RING (Chfr) is a ubiquitin ligase (E3) that establishes an antephase or prometaphase checkpoint in response to mitotic stress. Though ubiquitination is essential for checkpoint function, the sites, linkages and ubiquitin conjugating enzyme (E2) specificity are controversial. Here we dissect the function of the two Chfr homologs in S. cerevisiae, Chf1 and Chf2, overexpression of which retard cell cycle at both G(1) and G(2). Using a genetic assay, we establish that Ubc4 is required for Chf2-dependent G(1) cell cycle delay and Chf protein turnover. In contrast, Ubc13/Mms2 is required for G(2) delay and does not contribute to Chf protein turnover. By reconstituting cis and trans-ubiquitination activities of Chf proteins in purified systems and characterizing sites modified and linkages formed by tandem mass spectrometry, we discovered that Ubc13/Mms2- dependent modifications are a distinct subset of those catalyzed by Ubc4. Mutagenesis of Lys residues identified in vitro indicates that site-specific Ubc4-dependent Chf protein autoubiquitination is responsible for Chf protein turnover. Thus, combined genetic and biochemical analyses indicate that Chf proteins have dual E2 specificity accounting for different functions in the cell cycle.

Pubmed ID: 18202552


  • Loring GL
  • Christensen KC
  • Gerber SA
  • Brenner C


Cell cycle (Georgetown, Tex.)

Publication Data

January 1, 2008

Associated Grants

  • Agency: NCRR NIH HHS, Id: P20 RR018787
  • Agency: PHS HHS, Id: P20-018787
  • Agency: NCI NIH HHS, Id: P30 CA023108
  • Agency: NIGMS NIH HHS, Id: R01 GM081665
  • Agency: NIGMS NIH HHS, Id: R01 GM081665-01
  • Agency: PHS HHS, Id: R01-081665
  • Agency: NCI NIH HHS, Id: T32-CA09658

Mesh Terms

  • Amino Acid Sequence
  • Basic Helix-Loop-Helix Transcription Factors
  • Cell Cycle
  • Cell Cycle Proteins
  • Cell Division
  • G1 Phase
  • G2 Phase
  • Neoplasm Proteins
  • Repressor Proteins
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Structural Homology, Protein
  • Ubiquitin-Conjugating Enzymes
  • Ubiquitin-Protein Ligases
  • Ubiquitination