Question

You have a temperature sensitive mutant gene in a yeast. At restrictive (high) temperature it lead to hyperactivity. At permissive (low) temperature it functions normally. However, at restrictive temperature the cells do complete mitosis, but are very small. Which of the following protein is likely affected by the mutation.

A) Wee1kinase
B) p21
C) cdc 25 phosphatase
D) cdc 20

Answer 1

A) Wee1 kinase might be affected by mutation since temperature sensitive cells exhibit very small size upon mitosis.Wee 1 inhibits premature mitosis until a required cell size has been attained.It controls Cdc2 activity, and imposes a G2 arrest till minimum size required for mitosis has reached.

B) p21 activates a kinase that regulates yeast morphogenesis , promote budding and cytokinesis (cell division).This also might be affected by mutation.

C) cdc 25 phosphatase might not be affected by the mutation. Cdc 25 phosphatases activate CDKs (cyclin dependent kinases) via dephosphorylation and are required for G1 to S phase transition followed by entry into mitosis.Since the mutation shows mitosis is completed , but cell size is small, so this protein is not affected by mutation.

D) cdc 20 has a role in meiosis at spindle checkpoints. It is not likely to affected by the mutation.