title: An APC/C-Cdh1 Biosensor Reveals the Dynamics of Cdh1 Inactivation at the G1/S Transition.
abstract: B-type cyclin-dependent kinase activity must be turned off for mitotic exit and G1 stabilization. B-type cyclin degradation is mediated by the anaphase-promoting complex/cyclosome (APC/C); during and after mitotic exit, APC/C is dependent on Cdh1. Cdh1 is in turn phosphorylated and inactivated by cyclin-CDK at the Start transition of the new cell cycle. We developed a biosensor to assess the cell cycle dynamics of APC/C-Cdh1. Nuclear exit of the G1 transcriptional repressor Whi5 is a known marker of Start; APC/C-Cdh1 is inactivated 12 min after Whi5 nuclear exit with little measurable cell-to-cell timing variability. Multiple phosphorylation sites on Cdh1 act in a redundant manner to repress its activity. Reducing the number of phosphorylation sites on Cdh1 can to some extent be tolerated for cell viability, but it increases variability in timing of APC/C-Cdh1 inactivation. Mutants with minimal subsets of phosphorylation sites required for viability exhibit striking stochasticity in multiple responses including budding, nuclear division, and APC/C-Cdh1 activity itself. Multiple cyclin-CDK complexes, as well as the stoichiometric inhibitor Acm1, contribute to APC/C-Cdh1 inactivation; this redundant control is likely to promote rapid and reliable APC/C-Cdh1 inactivation immediately following the Start transition.
authors.affiliation: Laboratory of Cell Cycle Genetics, The Rockefeller University, New York, NY 10065, United States of America.
authors.forename: Andrej
authors.initials: A
authors.lastname: Ondracka
authors.affiliation: Laboratory of Cell Cycle Genetics, The Rockefeller University, New York, NY 10065, United States of America.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Robbins
authors.affiliation: Laboratory of Cell Cycle Genetics, The Rockefeller University, New York, NY 10065, United States of America.
authors.forename: Frederick R
authors.initials: FR
authors.lastname: Cross
mesh_terms: D064173:Anaphase-Promoting Complex-Cyclosome / Q000378:metabolism*; D001426:Bacterial Proteins; D015374:Biosensing Techniques / Q000379:methods*; D064200:Cdh1 Proteins / Q000235:genetics / Q000378:metabolism*; D059447:Cell Cycle Checkpoints / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D028884:Karyopherins / Q000378:metabolism; D008164:Luminescent Proteins; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D010766:Phosphorylation; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C516306:Acm1 protein, S cerevisiae; C472767:Ase1 protein, S cerevisiae; D001426:Bacterial Proteins; C577583:CDH1 protein, S cerevisiae; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; D019926:Cyclin B; D028884:Karyopherins; D008164:Luminescent Proteins; C401306:MSN5 protein, S cerevisiae; D008869:Microtubule-Associated Proteins; D029701:Saccharomyces cerevisiae Proteins; C054562:yellow fluorescent protein, Bacteria; D064173:Anaphase-Promoting Complex-Cyclosome; D018844:Cyclin-Dependent Kinases