A . Mutation of Tppp1 protein sequence (T14A; S18A, S45A, and S160A) inhibited p

Question

A. Mutation of Tppp1 protein sequence (T14A; S18A, S45A, and S160A) inhibited phosphorylation of Tppp1 by CDK-Cyclin complexes, why? Rubric (2): Correct answer based on knowledge of amino acid chemistry)

Active Tppp1 destabilizes microtubules (Tppp1=MAP).

B. Researchers found that Tppp1 is inactive at the beginning of the G1/S transition (interphase).

Later in the cell cycle (G2àM) Tppp1 becomes active (entering mitosis).

Explain why changing the activity of Tppp1 (G1àS; inactive) vs G2àM (active) would support the difference in MT arrangement in the images above! Rubric (3): Explanation correctly ties Tppp1 inactive/active, its function, and difference in appearance of microtubules shown below (3).

Explanation / Answer

1. The 4 amino acids are important in the activity of Tppp1, the mutation of these amino acids prevented the substrates for Cyclin-CDK kinases for phosphorylation. The amino acids threonine and serine sre important for the phosphorylation to take place.

2. The microtubules in the interphase are stable as the chromosomes are not yet segregated while in the mitosis where the chromosome segreation takes place where they are separated to opposite. During this process the microtubules are to e destabilized to pull apart the two chromatids to opposite poles and they have to be activated by phosphorylation.

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