Published 30 January 2006. doi:10.1083/jcb.200507162
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 172, Number 3, 335-346
Disappearance of the budding yeast Bub2Bfa1 complex from the mother-bound spindle pole contributes to mitotic exit
Roberta Fraschini,
Claudio D'Ambrosio,
Marianna Venturetti,
Giovanna Lucchini, and
Simonetta Piatti
Dipartimento di Biotecnologie e Bioscienze, Universitá di Milano-Bicocca, 20126 Milano, Italy
Correspondence to Simonetta Piatti: simonetta.piatti{at}unimib.it
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.
Abbreviations used in this paper: FEAR, Cdc14 early anaphase release; GAP, GTPase-activating protein; GDP, guanosine 5'-diphosphate; MBP, maltose binding protein; MEN, mitotic exit network; SPB, spindle pole body.

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