Question: this problem deals with the mechanism by which the dna...
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This problem deals with the mechanism by which the DNA damage
checkpoint induces cell-cycle arrest before mitosis.
QUESTION 9-1 Briefly describe why it is
advantageous for a cell with damaged DNA to delay
mitosis.
In fission yeast entry into mitosis is regulated by the
phosphorylation status of Tyrsin-15 (=Y15) in Cdc2. This residue
can be phosphorylated by the two kinases Wee1 and Mik1, and
de-phosphorylated by the phosphatase Cdc25. Mitosis is triggered
when the phosphatase activity of Cdc25 overcomes the kinase
activity of Wee1/Mik1.
To determine if the checkpoint pathway inhibits mitosis by
targeting Cdc2 Y15 phosphorylation, cells with a Cdc2-Y15F mutation
were studied. These cell cells are viable but “wee” (small),
because Cdc2 cannot be phosphorylated on F15. Y15F cells and wild
type cells were synchronized in G2 by elutriation (a technique that
allows isolation of the small newborn cells) and irradiated, and
the kinetics of completion of mitosis was monitored (Figure 9-1).
Unirradiated cells of both strains were included as controls
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