Biology 2382B Lecture Notes - Lecture 8: Prophase, Proteasome, S Phase
Document Summary
Wee1 is a kinase that phosphorylates cdk leading to its inactivation, while cdc25 is a phosphatase that removes the inhibitory phosphate group (left by wee1) from cdk and promotes its activation. In the recessive elongated fission yeast cells, these mutants were long and unable to engage mitosis (increased. G2), because their mutation either resulted in an excess of wee1 or a deficit of cdc25 (leading to inappropriately inactive mpf). In the dominant premature fission yeast cells, these mutants were short and engaged mitosis unprepared (decreased g2), because their mutation either resulted in an excess of cdc25 or a deficit of wee1 (leading to prematurely activated mpf). When mitotic cyclin binds to the cdk, it initially forms an inactive mitosis promoting factor. Wee1, an inhibitory kinase, introduces a phosphate group to the tyrosine at position 15 (y15) on bound cdk, so the mpf complex remains inactive (key to discouraging premature mitosis).