title: Complex formation between Mad1p, Bub1p and Bub3p is crucial for spindle checkpoint function.
abstract: The spindle checkpoint delays the metaphase to anaphase transition in response to defects in kinetochore-microtubule interactions in the mitotic apparatus (see [1] [2] [3] [4] for reviews). The Mad and Bub proteins were identified as key components of the spindle checkpoint through budding yeast genetics [5] [6] and are highly conserved [3]. Most of the spindle checkpoint proteins have been localised to kinetochores, yet almost nothing is known about the molecular events which take place there. Mad1p forms a tight complex with Mad2p [7], and has been shown to recruit Mad2p to kinetochores [8]. Similarly, Bub3p binds to Bub1p [9] and may target it to kinetochores [10]. Here, we show that budding yeast Mad1p has a regulated association with Bub1p and Bub3p during a normal cell cycle and that this complex is found at significantly higher levels once the spindle checkpoint is activated. We find that formation of this complex requires Mad2p and Mps1p but not Mad3p or Bub2p. In addition, we identify a conserved motif within Mad1p that is essential for Mad1p-Bub1p-Bub3p complex formation. Mutation of this motif abolishes checkpoint function, indicating that formation of the Mad1p-Bub1p-Bub3p complex is a crucial step in the spindle checkpoint mechanism.
authors.affiliation: Wellcome Trust Centre for Cell Biology, Institute of Cell and Molecular Biology, University of Edinburgh, UK.
authors.forename: D M
authors.initials: DM
authors.lastname: Brady
authors.forename: K G
authors.initials: KG
authors.lastname: Hardwick
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism; D017124:Conserved Sequence; D005656:Fungal Proteins / Q000378:metabolism; D006801:Humans; D008870:Microtubules / Q000502:physiology; D008938:Mitosis; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000075223:Poly-ADP-Ribose Binding Proteins; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000378:metabolism*; D012097:Repressor Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D008941:Spindle Apparatus / Q000502:physiology*
chemical_list: C070352:BUB3 protein, S cerevisiae; C489444:BUB3 protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D005656:Fungal Proteins; C501382:MAD1 protein, S cerevisiae; C501384:MAD1L1 protein, human; D009687:Nuclear Proteins; D010750:Phosphoproteins; D000075223:Poly-ADP-Ribose Binding Proteins; D011506:Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; C090464:Bub1 spindle checkpoint protein; D017346:Protein Serine-Threonine Kinases