Mutant Saccharomyces Cerevisiae Cells That Lack the Gene Encoding Securin

question 9

Multiple Choice

Mutant Saccharomyces cerevisiae cells that lack the gene encoding securin can divide more or less normally by mitosis, without significant chromosome segregation defects. Cells harboring a nondegradable version of securin, on the other hand, arrest in metaphase as expected, since they cannot activate separase to enter anaphase. Similarly, cells lacking Cdc20 arrest in metaphase, since they cannot activate APC/C. Finally, cells lacking both securin and Cdc20 arrest in anaphase: they manage to separate sister chromatids, but do not progress much further. These results suggest that in wild-type cells, …

• A) degradation of securin is necessary to trigger sister-chromatid separation.
• B) degradation of securin is sufficient to trigger sister-chromatid separation.
• C) Cdc20-APC/C is NOT necessary for sister-chromatid separation.
• D) Cdc20-APC/C is NOT necessary for later events in anaphase.
• E) All of the above.

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