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- A New Function of Skp1 in the Mitotic Exit of Budding Yeast Saccharomyces cerevisiae
- Namil Kim , Hayoung Yoon , Eunhwa Lee , Kiwon Song
- J. Microbiol. 2006;44(6):641-648.
- DOI: https://doi.org/2463 [pii]
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Abstract
- We previously reported that Skp1, a component of the Skp1-Cullin-F-box protein (SCF) complex essential for the timely degradation of cell cycle proteins by ubiquitination, physically interacts with Bfa1, which is a key negative regulator of the mitotic exit network (MEN) in response to diverse checkpoint-activating stresses in budding yeast. In this study, we initially investigated whether the interaction of Skp1 and Bfa1 is involved in the regulation of the Bfa1 protein level during the cell cycle, especially by mediating its degradation. However, the profile of the Bfa1 protein did not change during the cell cycle in skp1-11, which is a SKP1 mutant allele in which the function of Skp1 as a part of SCF is completely impaired, thus indicating that Skp1 does not affect the degradation of Bfa1. On the other hand, we found that the skp1-12 mutant allele, previously reported to block G2-M transition, showed defects in mitotic exit and cytokinesis. The skp1-12 mutant allele <br><br>also revealed a specific genetic interaction with Δbfa1. Bfa1 interacted with Skp1 via its 184 C-terminal residues (Bfa1-D8) that are responsible for its function in mitotic exit. In addition, the interaction between Bfa1 and the Skp1-12 mutant protein was stronger than that of Bfa1 and the wild type Skp1. We suggest a novel function of Skp1 in mitotic exit and cytokinesis, independent of its function as a part of the SCF complex. The interaction of Skp1 and Bfa1 may contribute to the function of Skp1 in the mitotic exit.
- Characterization of a Putative F-box Motif in Ibd1p/Bfa1p, a Spindle Checkpoint Regulator of Budding Yeast Saccharomyces cerevisiae
- Kyum-Jung Lee , Hyung-Seo Hwang , Kiwon Song
- J. Microbiol. 2001;39(4):286-292.
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Abstract
- During mitosis, the proper segregation of duplicated chromosomes is coordinated by a spindle checkpoint. The bifurcated spindle checkpoint blocks cell cycle progression at metaphase by monitoring unattached kinetochores and inhibits mitotic exit in response to the misorientation of the mitotic spindle. Ibd1p/Bfa1p is a spindle checkpoint regulator of budding yeast in the Bub2p checkpoint pathway for mitotic exit and its disruption abolishes mitotic arrest when proper organization of the mitotic spindle is inhibited. Ibd1p/Bfa1p localizes to the spindle pole body, a microtubule-organizing center in yeast, and its overexpression arrests the cell cycle in 80% of cells with an enlarged bud at mitosis and in 20% of cells with multiple buds. In this study, we found that the C-terminus of Ibd1p/Bfa1p physically interacts with Skp1p, a key component of SCF (Skp1/cullin/F-box) complex for ubiquitin-mediated proteolysis of cell cycle regulators as well as an evolutionally conserved kinetochore protein for cell cycle progression. A putative F-box motif was found in the C-terminus of Ibd1p/Bfa1p and its function was investigated by making mutants of conserved residues in the motif. These Ibd1p/Bfa1p mutants of a putative F-box interacted with Skp1p in vitro by two-hybrid assays as wild type Ibd1p/Bfa1p. Also, these Ibd1p/Bfa1p mutants displayed the overexpression phenotypes of wild type Ibd1p, when over-expressed under inducible promoters. These results suggest that a putative F-box motif of Ibd1p/Bfa1p is not essential for the interaction with Skp1p and its function in mitotic exit and cytokinesis.
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