Figure 2

A model for control over mitotic exit by the spindle position checkpoint. See text for details. In the presence of misaligned spindle Kin4 and the Bub2/Bfa1 complex are retained at both SPBs and prevent mitotic exit by inhibiting Tem1. When the spindle is correctly positioned, passage of one SPB through the bud neck leads to disappearance of Bub2/Bfa1 from the mother cell SPB and to the exposure of the pool of Tem1 located on the daughter cell SPB to its activator Lte1. At the same time both Tem1 and the Bub2/Bfa1 complex get concentrated on the bud-directed SPB. During this stage the polo kinase Cdc5 phosphorylates Bub2/Bfa1, although at the moment it is unclear where in the cell this regulation takes place. In late anaphase Bub2/Bfa1 disappears also from the daughter cell SPB, whereas Kin4 is removed from the mother-bound SPB. Concomitantly, Lte1 diffuses into the cytoplasm of both mother and daughter cell. Probably, all these events contribute to promote MEN activation. Kin4 localization at the bud neck in late anaphase is not depicted.