B-Cyclin/CDKs regulate mitotic spindle assembly by phosphorylating kinesins-5 in budding yeast
Abstract
Although it has been known for many years that B-cyclin/CDK complexes regulate the
assembly of the mitotic spindle and entry into mitosis, the full complement of relevant
CDK targets has not been identified. It has previously been shown in a variety of
model systems that B-type cyclin/CDK complexes, kinesin-5 motors, and the SCFCdc4
ubiquitin ligase are required for the separation of spindle poles and assembly of
a bipolar spindle. It has been suggested that, in budding yeast, B-type cyclin/CDK
(Clb/Cdc28) complexes promote spindle pole separation by inhibiting the degradation
of the kinesins-5 Kip1 and Cin8 by the anaphase-promoting complex (APCCdh1). We have
determined, however, that the Kip1 and Cin8 proteins are present at wild-type levels
in the absence of Clb/Cdc28 kinase activity. Here, we show that Kip1 and Cin8 are
in vitro targets of Clb2/Cdc28 and that the mutation of conserved CDK phosphorylation
sites on Kip1 inhibits spindle pole separation without affecting the protein's in
vivo localization or abundance. Mass spectrometry analysis confirms that two CDK sites
in the tail domain of Kip1 are phosphorylated in vivo. In addition, we have determined
that Sic1, a Clb/Cdc28-specific inhibitor, is the SCFCdc4 target that inhibits spindle
pole separation in cells lacking functional Cdc4. Based on these findings, we propose
that Clb/Cdc28 drives spindle pole separation by direct phosphorylation of kinesin-5
motors. © 2010 Chee, Haase.
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https://hdl.handle.net/10161/4466Published Version (Please cite this version)
10.1371/journal.pgen.1000935Publication Info
Chee, Mark K; & Haase, Steven B (2010). B-Cyclin/CDKs regulate mitotic spindle assembly by phosphorylating kinesins-5 in budding
yeast. PLoS Genetics, 6(5). pp. 35. 10.1371/journal.pgen.1000935. Retrieved from https://hdl.handle.net/10161/4466.This is constructed from limited available data and may be imprecise. To cite this
article, please review & use the official citation provided by the journal.
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Steven B. Haase
Professor of Biology
Our group is broadly interested in understanding the biological clock mechanisms that
control the timing of events during the cell division cycle. In 2008, the Haase group
proposed a new model in which a complex network of sequentially activated transcription
factors regulates the precise timing of gene expression during the cell-cycle, and
functions as a robust time-keeping oscillator. Greater than a thousand genes are expressed
at distinct phases of the cycle, and the control network itself

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