Stu1 inversely regulates kinetochore capture and spindle stability
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↵1 These authors contributed equally to this work.
Abstract
The Saccharomyces cerevisiae CLASP (CLIP-associated protein) Stu1 is essential for the establishment and maintenance of the mitotic spindle. Furthermore, Stu1 localizes to kinetochores. Here we show that, in prometaphase, Stu1 assembles in an Ndc80-dependent manner exclusively at kinetochores that are not attached to microtubules. Stu1 relocates to microtubules when a captured kinetochore reaches a spindle pole. This relocation does not depend on kinetochore biorientation, but requires a functional DASH complex. Stu1 at detached kinetochores facilitates kinetochore capturing. Furthermore, since most of the nuclear Stu1 is sequestered by one or a few detached kinetochores, the presence of detached kinetochores prevents Stu1 from localizing the spindle, and therefore from stabilizing the spindle. Thus, the sequestering of Stu1 by detached kinetochores serves as a checkpoint that keeps spindle poles in close proximity until all kinetochores are captured. This is likely to facilitate kinetochore biorientation. In agreement with the findings described above, a kinetochore mutant (okp1-52) that fails to release Stu1 from the kinetochore displays a severe spindle defect upon spindle pole body separation, and this defect can be rescued by destroying the okp1-52 kinetochore.
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Footnotes
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↵2 Corresponding author.
E-MAIL johannes.lechner{at}bzh.uni-heidelberg.de; FAX 49-6221-544366.
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Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.541309.
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Supplemental material is available at http://www.genesdev.org.
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- Received May 29, 2009.
- Accepted October 12, 2009.
- Copyright © 2009 by Cold Spring Harbor Laboratory Press