The Mck1 GSK-3 kinase inhibits the activity of Clb2-Cdk1 post-nuclear division.
The glycogen synthase kinase-3 homolog, Mck1, has been implicated in many cellular functions, from sporulation to calcium stress response in budding yeast. Here, we report a novel function for Mck1 in the inhibition of Clb2-Cdk1 activity post nuclear division. Clb2-Cdk1, the major mitotic cyclin-Cdk complex in yeast, accumulates before anaphase and must be inhibited in telophase for cells to exit mitosis and enter into the next cell cycle. We show that the mck1Δ mutant is highly sensitive to increased Clb2-Cdk1 activity caused either by overexpression of Clb2 or the Cdk1-activating phosphatase Mih1. Deletion of the Cdk1 inhibitory kinase, SWE1, in combination with a mck1Δ mutant results in a synthetic growth defect, suggesting that Mck1 and Swe1 function in parallel pathways to inhibit Clb2-Cdk1. We find that mck1Δ strains have a delay in mitotic exit as well as elevated levels of Clb2-Cdk1 activity post-nuclear division. Using a co-immunoprecipitation assay, we identify a physical interaction between Mck1 and both Clb2 and Mih1. Finally, we demonstrate that phosphorylation of purified Clb2 by Cdk1 is inhibited by catalytically active Mck1 but not catalytically inactive Mck1 in vitro. We propose that Mck1 inhibits the activity of Clb2-Cdk1 via interaction with Clb2. The mammalian glycogen synthase kinase-3 homolog has been implicated in cyclin inhibition, suggesting a conserved cell cycle function for both yeast and mammalian glycogen synthase kinases.
Genetics Graduate Program; University of British Columbia; Vancouver, BC Canada.
Jennifer
J
McQueen
Dewald
D
van Dyk
Barry
B
Young
Chris
C
Loewen
Vivien
V
Measday
D017489:CDC28 Protein Kinase, S cerevisiae / Q000378:metabolism*; D002455:Cell Division; D002467:Cell Nucleus / Q000378:metabolism*; D019926:Cyclin B / Q000378:metabolism*; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism*; D008938:Mitosis; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000201:enzymology* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
C093749:CLB2 protein, S cerevisiae; D019926:Cyclin B; D029701:Saccharomyces cerevisiae Proteins; D017489:CDC28 Protein Kinase, S cerevisiae; D038362:Glycogen Synthase Kinase 3; C068124:MCK1 protein, S cerevisiae