You are characterizing a temperature-sensitive mutant called nlk1 in Saccharomyc

Question

You are characterizing a temperature-sensitive mutant called nlk1 in Saccharomyces cerevisiae. To examine whether the mutant has a defect in cell cycle progression, you perform two experiments. First, you try flow cytometry with samples of the mutant strain incubated at the permissive or non-permissive temperatures. A wildtype strain incubated at each temperature is a used as control. The flow cytometry results are shown below in Panel A. Second, you examine the Nlk1 protein levels throughout the cell cycle in a synchronized cell population when the cells are incubated at a semi-permissive temperature (i.e., conditions where the mutant nlk1 protein is partially inactivated). Again, you use wildtype Nlk1 as a control (wildtype Nlk1 is functional at this temperature) and examine whether there are differences with the mutant nlk1 protein. The protein results are shown in Panel B.

A) Does the nlk1 mutant have a cell cycle defect? If so, at which cell cycle transition is it defective? Provide a short explanation for your answer.

B) How does the regulation of the mutant nlk1 protein levels differ throughout the cell cycle compared to the wildtype Nlk1 protein? What does this suggest about how the wildtype Nlk1 protein is regulated? What do you predict the mutation in the defective nlk1 protein does?

C) Based on your answer in B, suggest an experiment that would test your hypothesis about the regulation of the Nlk1 protein.

Explanation / Answer

Yes, the nlk1 mutant have a cell cycle defect. It is defective at M phase of the cell cycle, which is the most dramatic period involving a major reorganization of virtually all cell components. Observing the panel B, we could see a change at M phase.

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