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17 - MIC170 Lecture 17(Thursday 5/28 Continued on Cell...

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Unformatted text preview: MIC170 5/28/09 Lecture 17 (Thursday, 5/28) Continued on Cell cycle control Additional Regulatory factors at the G2/M transition --- Wee1 and Cdc25 1. wee1ts mutant in fission yeast ----- discussed in the last lecture 2. cdc25ts mutant (Fig. 4-5 in handout-9) ----> at 37oC, cells arrest in G2 and cannot initiate mitosis, like cdc2ts cdc25+ gene was cloned similarity to protein phosphatase multicopy of cdc25+ gene -- advanced mitosis (wee phenotype) (Fig. 4-9 in handout 9) Thus, Cdc25 is a positive regulator of mitotic initiation. Relationship between cdc25 and cdc2? cdc2-3w cdc25 double mutant ----- similar to the cdc2-3w single mutant (divide at ~8 m) cdc2-3w carrying multicopy cdc25+ ----- similar to cdc2-3w Cdc25 positively functions upstream of Cdc2 Cdc25 Cdc2 G2 M 1 MIC170 5/28/09 Relationship between wee1 and cdc25? cdc25 wee1 double mutant ----- divide at normal cell length (Fig. 4-5, handout 9; double mutant phenotype is different from those of the single mutants) Cdc25 and Wee1 independently regulate Cdc2 Cdc25 Wee1 Cdc2 G2 M Subsequent biochemical studies demonstrated that the Wee1 kinase inhibits Cdc2 by direct phosphorylation of Tyr-15 in Cdc2. At the end of the G2 phase, this inhibitory phosphorylation on Cdc2 is removed by the Cdc25 phosphatase, so that the activated Cdc2-cyclin complex can induce mitosis. Wee1 and Cdc25 are also conserved in human cells and regulate Cdc2 (CDK) at the entry into mitosis. 2 ...
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