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.
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Evidence ID | Analyze ID | Interactor | Interactor Systematic Name | Interactor | Interactor Systematic Name | Allele | Assay | Annotation | Action | Phenotype | SGA score | P-value | Source | Reference | Note |
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Increase the total number of rows showing on this page by using the pull-down located below the table, or use the page scroll at the table's top right to browse through the table's pages; use the arrows to the right of a column header to sort by that column; filter the table using the "Filter" box at the top of the table; click on the small "i" buttons located within a cell for an annotation to view further details about experiment type and any other genes involved in the interaction.
Interactor | Interactor | Assay | Annotation | Action | Modification | |
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ASH1 | CDC4 | Reconstituted Complex | manually curated | Bait-Hit | No Modification | |
ASH1 | CDC4 | Biochemical Activity | manually curated | Hit-Bait | ubiquitinylated lysine | |
Ash1 phospho-peptides interacted with Cdc4|Figure 10 | ASH1 | CDC4 | Protein-peptide | manually curated | Hit-Bait | No Modification |
Figure 7 | ASH1 | PHO85 | Biochemical Activity | manually curated | Hit-Bait | phosphorylated residue |
CDC28 | ASH1 | Biochemical Activity | manually curated | Bait-Hit | phosphorylated residue | |
Figure 9 | CDC34 | HRT1 | Reconstituted Complex | manually curated | Hit-Bait | No Modification |