title: SCFCdc4 enables mating type switching in yeast by cyclin-dependent kinase-mediated elimination of the Ash1 transcriptional repressor.
abstract: In the budding yeast Saccharomyces cerevisiae, mother cells switch mating types between a and α forms, whereas daughter cells do not. This developmental asymmetry arises because the expression of the HO endonuclease, which initiates the interconversion of a and α mating type cassettes, is extinguished by the daughter-specific Ash1 transcriptional repressor. When daughters become mothers in the subsequent cell cycle, Ash1 must be eliminated to enable a new developmental state. Here, we report that the ubiquitin ligase SCF(Cdc4) mediates the phosphorylation-dependent elimination of Ash1. The inactivation of SCF(Cdc4) stabilizes Ash1 in vivo, and consistently, Ash1 binds to and is ubiquitinated by SCF(Cdc4) in a phosphorylation-dependent manner in vitro. The mutation of a critical in vivo cyclin-dependent kinase (CDK) phosphorylation site (Thr290) on Ash1 reduces its ubiquitination and rate of degradation in vivo and decreases the frequency of mating type switching. Ash1 associates with active Cdc28 kinase in vivo and is targeted to SCF(Cdc4) in a Cdc28-dependent fashion in vivo and in vitro. Ash1 recognition by Cdc4 appears to be mediated by at least three phosphorylation sites that form two redundant diphosphorylated degrons. The phosphorylation-dependent elimination of Ash1 by the ubiquitin-proteasome system thus underpins developmental asymmetry in budding yeast.
authors.affiliation: School of Biological Sciences, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, United Kingdom.
authors.forename: Qingquan
authors.initials: Q
authors.lastname: Liu
authors.forename: Brett
authors.initials: B
authors.lastname: Larsen
authors.forename: Marketa
authors.initials: M
authors.lastname: Ricicova
authors.forename: Stephen
authors.initials: S
authors.lastname: Orlicky
authors.forename: Hille
authors.initials: H
authors.lastname: Tekotte
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Tang
authors.forename: Karen
authors.initials: K
authors.lastname: Craig
authors.forename: Adam
authors.initials: A
authors.lastname: Quiring
authors.forename: Thierry
authors.initials: T
authors.lastname: Le Bihan
authors.forename: Carl
authors.initials: C
authors.lastname: Hansen
authors.forename: Frank
authors.initials: F
authors.lastname: Sicheri
authors.forename: Mike
authors.initials: M
authors.lastname: Tyers
mesh_terms: D000595:Amino Acid Sequence; D017489:CDC28 Protein Kinase, S cerevisiae / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D044783:F-Box Proteins / Q000378:metabolism*; D020868:Gene Silencing; D049770:Genes, Mating Type, Fungal; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010769:Phosphothreonine / Q000378:metabolism; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D055550:Protein Stability; D021381:Protein Transport; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000201:enzymology* / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D014158:Transcription, Genetic; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C098733:ASH1 protein, S cerevisiae; C080443:CDC4 protein, S cerevisiae; D018797:Cell Cycle Proteins; D044783:F-Box Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D010769:Phosphothreonine; D044767:Ubiquitin-Protein Ligases; D017489:CDC28 Protein Kinase, S cerevisiae; D018844:Cyclin-Dependent Kinases