Yeni bir mitozdan çıkış inhibitörünün moleküler rolünün ekmek mayasında karakterizasyonu

Saccharomyces cerevisiae, also known as the budding yeast, is an ideal model for investigation of how spindle orientation impinges on asymmetric cell division. Every cell division in S. cerevisiae is asymmetric, giving rise to a young daughter and an old mother cell with distinct fates. The budding yeast, orients and elongates its mitotic spindle along its polarity axis in order to segregate one copy of its genomic DNA to the daughter cell. If accurate positioning of the mitotic spindle fails, a surveillance mechanism, named the Spindle POsition Checkpoint (SPOC), prevents cells from exiting mitosis unless the spindle orientation is corrected. Such mitotic arrest provides cells time to align their spindle correctly before cell division is completed. Mutants with a defective SPOC loss their genomic integrity, become multiploid and aneuploid. Thus, SPOC is a crucial checkpoint for the budding yeast. Yet, a comprehensive understanding of how SPOC mechanism works is lacking. In this study, we identified Bud14 as a novel checkpoint protein. We showed that Bud14 in association with the type 1 protein phosphatase, Glc7, has a mitotic exit inhibitory function. bud14∆ cells accumulated multinucleated phenotypes when spindle positioning was impaired in these cells. In addition, deletion of BUD14 promoted growth of mutants defective in mitotic exit. The function of Bud14 in SPOC dependent on its ability to bind Glc7. Cells bearing versions of Bud14 that cannot interact with Glc7 was SPOC deficient. Furthermore, they were unable to rescue growth of mitotic exit mutants. Mitotic exit inhibitory role of Bud14 was not through its role in formin regulation as a Bud14 mutant that cannot bind to the formin Bnr1 was functional in terms of mitotic exit inhibition. Our data indicate that Bud14-Glc7 inhibits mitotic exit by promoting dephosphorylation of Bfa1 during anaphase. Our results support a model in which Bud14-Glc7 works parallel to the SPOC kinase Kin4 in regulating Bfa1, the most downstream effector of SPOC that inhibits mitotic exit.