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Mol. Cell. Biol., 05 1997, 2723-2734, Vol 17, No. 5
X Li and M Cai
Eukaryotic cells may halt cell cycle progression following exposure to
certain exogenous agents that damage cellular structures such as DNA or
microtubules. This phenomenon has been attributed to functions of cellular
control mechanisms termed checkpoints. Studies with the fission yeast
Schizosaccharomyces pombe and mammalian cells have led to the conclusion
that cell cycle arrest in response to inhibition of DNA replication or DNA
damage is a result of down-regulation of the cyclin- dependent kinases
(CDKs). Based on these studies, it has been proposed that inhibition of the
CDK activity may constitute a general mechanism for checkpoint controls.
Observations made with the budding yeast Saccharomyces cerevisiae, however,
appear to disagree with this model. It has been shown that high levels of
mitotic CDK activity are present in the budding yeast cells arrested in
G2/mitosis as the result of DNA damage or replication inhibition. In this
report, we show that a novel mutant allele of the CDC28 gene, encoding the
budding yeast CDK, allowed cell cycle passage through mitosis and nuclear
division in the presence of DNA damage and the microtubule toxin nocodazole
at a restrictive temperature. Unlike the checkpoint-defective mutations in
CDKs of fission yeast and mammalian cells, the cdc28 mutation that we
identified was recessive and resulted in a loss of the CDK activity,
including the Clb2-, Clb5-, and Clb6-associated, but not the Clb3-
associated, CDK activities. Examination of several known alleles of cdc28
revealed that they were also, albeit partially, defective in cell cycle
arrest in response to UV-generated DNA damage. These findings suggest that
Cdc28 kinase in budding yeast may be required for cell cycle arrest
resulting from DNA damage and disassembly of mitotic spindles.
Copyright © 1997, American Society for Microbiology
Inactivation of the cyclin-dependent kinase Cdc28 abrogates cell cycle arrest induced by DNA damage and disassembly of mitotic spindles in Saccharomyces cerevisiae
Institute of Molecular and Cell Biology, National University of Singapore.
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