The Bfa1/Bub2 GAP complex comprises a universal checkpoint required to prevent mitotic exit.
At the end of the cell cycle, cyclin-dependent kinase (CDK) activity is inactivated to allow mitotic exit [1]. A protein phosphatase, Cdc14, plays a key role during mitotic exit in budding yeast by activating the Cdh1 component of the anaphase-promoting complex to degrade cyclin B (Clb) and inducing the CDK inhibitor Sic1 to inactivate Cdk1 [2]. To prevent mitotic exit when the cell cycle is arrested at G2/M, cells must prevent CDK inactivation. In the spindle checkpoint pathway, this is accomplished through Bfa1/Bub2, a heteromeric GTPase-activating protein (GAP) that inhibits Clb degradation by keeping the G protein Tem1 inactive [3-5]. Tem1 is required for Cdc14 activation. Here we show that in budding yeast, BUB2 and BFA1 are also required for the maintenance of G2/M arrest in response to DNA damage and to spindle misorientation. cdc13-1 bub2 and cdc13-1 bfa1 but not cdc13-1 mad2 double mutants rebud and reduplicate their DNA at the restrictive temperature. We also found that the delay in mitotic exit in mutants with misoriented spindles depended on BUB2 and BFA1, but not on MAD2. We propose that Bfa1/Bub2 checkpoint pathway functions as a universal checkpoint in G2/M that prevents CDK inactivation in response to cell-cycle delay in G2/M.
Wang
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Verna and Mars McLean Department of Biochemistry and Molecular Biology, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas 77030, USA.
Hu
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Elledge
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D000199:Actins / Q000235:genetics / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D019926:Cyclin B / Q000235:genetics / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D020549:GTP Phosphohydrolase Activators / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D018816:Genes, cdc; D064246:Mad2 Proteins; D008869:Microtubule-Associated Proteins; D008938:Mitosis / Q000235:genetics*; D009154:Mutation; D009687:Nuclear Proteins; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D008941:Spindle Apparatus / Q000378:metabolism; D013696:Temperature
C089021:ARP1 protein, S cerevisiae; D000199:Actins; C119117:BFA1 protein, S cerevisiae; C070351:BUB2 protein, S cerevisiae; C074860:CDC14 protein, S cerevisiae; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019926:Cyclin B; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins; D020549:GTP Phosphohydrolase Activators; D020690:GTPase-Activating Proteins; C086450:JNM1 protein, S cerevisiae; C501382:MAD1 protein, S cerevisiae; C501384:MAD1L1 protein, human; C577695:MAD2 protein, S cerevisiae; D064246:Mad2 Proteins; D008869:Microtubule-Associated Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D018844:Cyclin-Dependent Kinases; D017027:Protein Tyrosine Phosphatases