title: A yeast GSK-3 kinase Mck1 promotes Cdc6 degradation to inhibit DNA re-replication.
abstract: Cdc6p is an essential component of the pre-replicative complex (pre-RC), which binds to DNA replication origins to promote initiation of DNA replication. Only once per cell cycle does DNA replication take place. After initiation, the pre-RC components are disassembled in order to prevent re-replication. It has been shown that the N-terminal region of Cdc6p is targeted for degradation after phosphorylation by Cyclin Dependent Kinase (CDK). Here we show that Mck1p, a yeast homologue of GSK-3 kinase, is also required for Cdc6 degradation through a distinct mechanism. Cdc6 is an unstable protein and is accumulated in the nucleus only during G1 and early S-phase in wild-type cells. In mck1 deletion cells, CDC6p is stabilized and accumulates in the nucleus even in late S phase and mitosis. Overexpression of Mck1p induces rapid Cdc6p degradation in a manner dependent on Threonine-368, a GSK-3 phosphorylation consensus site, and SCF(CDC4). We show evidence that Mck1p-dependent degradation of Cdc6 is required for prevention of DNA re-replication. Loss of Mck1 activity results in synthetic lethality with other pre-RC mutants previously implicated in re-replication control, and these double mutant strains over-replicate DNA within a single cell cycle. These results suggest that a GSK3 family protein plays an unexpected role in preventing DNA over-replication through Cdc6 degradation in Saccharomyces cerevisiae. We propose that both CDK and Mck1 kinases are required for Cdc6 degradation to ensure a tight control of DNA replication.
authors.affiliation: Department of Biology, Brooklyn College, The City University of New York, Brooklyn, New York, United States of America. AIkui@brooklyn.cuny.edu
authors.forename: Amy E
authors.initials: AE
authors.lastname: Ikui
authors.forename: Valentina
authors.initials: V
authors.lastname: Rossio
authors.forename: Lea
authors.initials: L
authors.lastname: Schroeder
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yoshida
mesh_terms: D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002467:Cell Nucleus / Q000235:genetics; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D008938:Mitosis; D059748:Proteolysis; D016196:S Phase / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C066503:CDC6 protein, S cerevisiae; D018797:Cell Cycle Proteins; D029701:Saccharomyces cerevisiae Proteins; D018844:Cyclin-Dependent Kinases; D038362:Glycogen Synthase Kinase 3; C068124:MCK1 protein, S cerevisiae