title: Regulation of cyclin-substrate docking by a G1 arrest signaling pathway and the Cdk inhibitor Far1.
abstract: Eukaryotic cell division is often regulated by extracellular signals. In budding yeast, signaling from mating pheromones arrests the cell cycle in G1 phase. This arrest requires the protein Far1, which is thought to antagonize the G1/S transition by acting as a Cdk inhibitor (CKI), although the mechanisms remain unresolved. Recent studies found that G1/S cyclins (Cln1 and Cln2) recognize Cdk substrates via specific docking motifs, which promote substrate phosphorylation in vivo. Here, we show that these docking interactions are inhibited by pheromone signaling and that this inhibition requires Far1. Moreover, Far1 mutants that cannot inhibit docking are defective at cell-cycle arrest. Consistent with this arrest function, Far1 outcompetes substrates for association with G1/S cyclins in vivo, and it is present in large excess over G1/S cyclins during the precommitment period where pheromone can impose G1 arrest. Finally, a comparison of substrates that do and do not require docking suggests that Far1 acts as a multimode inhibitor that antagonizes both kinase activity and substrate recognition by Cln1/2-Cdk complexes. Our findings uncover a novel mechanism of Cdk regulation by external signals and shed new light on Far1 function to provide a revised view of cell-cycle arrest in this model system.
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Pope
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA.
authors.forename: Samyabrata
authors.initials: S
authors.lastname: Bhaduri
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA 01605, USA. Electronic address: peter.pryciak@umassmed.edu.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Pryciak
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D050756:Cyclin-Dependent Kinase Inhibitor Proteins / Q000235:genetics* / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase; D015966:Gene Expression Regulation, Fungal; D010675:Pheromones / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C081185:CKS1 protein, S cerevisiae; D018797:Cell Cycle Proteins; D050756:Cyclin-Dependent Kinase Inhibitor Proteins; D016213:Cyclins; C081353:FAR1 protein, S cerevisiae; D010675:Pheromones; D029701:Saccharomyces cerevisiae Proteins; D018844:Cyclin-Dependent Kinases