title: Disappearance of the budding yeast Bub2-Bfa1 complex from the mother-bound spindle pole contributes to mitotic exit.
abstract: Budding yeast spindle position checkpoint is engaged by misoriented spindles and prevents mitotic exit by inhibiting the G protein Tem1 through the GTPase-activating protein (GAP) Bub2/Bfa1. Bub2 and Bfa1 are found on both duplicated spindle pole bodies until anaphase onset, when they disappear from the mother-bound spindle pole under unperturbed conditions. In contrast, when spindles are misoriented they remain symmetrically localized at both SPBs. Thus, symmetric localization of Bub2/Bfa1 might lead to inhibition of Tem1, which is also present at SPBs. Consistent with this hypothesis, we show that a Bub2 version symmetrically localized on both SPBs throughout the cell cycle prevents mitotic exit in mutant backgrounds that partially impair it. This effect is Bfa1 dependent and can be suppressed by high Tem1 levels. Bub2 removal from the mother-bound SPB requires its GAP activity, which in contrast appears to be dispensable for Tem1 inhibition. Moreover, it correlates with the passage of one spindle pole through the bud neck because it needs septin ring formation and bud neck kinases.
authors.affiliation: Dipartimento di Biotecnologie e Bioscienze, Universitá di Milano-Bicocca, 20126 Milano, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Fraschini
authors.forename: Claudio
authors.initials: C
authors.lastname: D'Ambrosio
authors.forename: Marianna
authors.initials: M
authors.lastname: Venturetti
authors.forename: Giovanna
authors.initials: G
authors.lastname: Lucchini
authors.forename: Simonetta
authors.initials: S
authors.lastname: Piatti
mesh_terms: D000483:Alleles; D000705:Anaphase / Q000235:genetics; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019926:Cyclin B / Q000378:metabolism; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D018844:Cyclin-Dependent Kinases / Q000235:genetics; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000187:drug effects / Q000235:genetics; D005799:Genes, Dominant / Q000235:genetics; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics; D008715:Methionine / Q000494:pharmacology; D008868:Microtubule Proteins / Q000235:genetics; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D008957:Models, Genetic; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010675:Pheromones / Q000494:pharmacology; D011494:Protein Kinases / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D017027:Protein Tyrosine Phosphatases / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008941:Spindle Apparatus / Q000378:metabolism / Q000502:physiology*
chemical_list: C119117:BFA1 protein, S cerevisiae; C119683:BIM1 protein, S cerevisiae; C070351:BUB2 protein, S cerevisiae; C074860:CDC14 protein, S cerevisiae; C093749:CLB2 protein, S cerevisiae; D018797:Cell Cycle Proteins; D019926:Cyclin B; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D003598:Cytoskeletal Proteins; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; C089357:LTE1 protein, S cerevisiae; D008868:Microtubule Proteins; D010675:Pheromones; C086926:SIC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C089965:TEM1 protein, S cerevisiae; D008715:Methionine; D011494:Protein Kinases; C099685:SWE1 protein, S cerevisiae; D011505:Protein-Tyrosine Kinases; C107283:GIN4 protein, S cerevisiae; C106494:HSL1 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; C081927:CDC5 protein, S cerevisiae; D016203:CDC2 Protein Kinase; D018844:Cyclin-Dependent Kinases; D017027:Protein Tyrosine Phosphatases; D020559:Monomeric GTP-Binding Proteins