The yeast Saccharomyces differentiates into filamentous pseudohyphae when exposed to a poor source of nitrogen in a process involving a collection of transcription factors regulated by nutrient signaling pathways. Phd1 is important for this process in that it regulates expression of most other transcription factors involved in differentiation and can induce filamentation on its own when overproduced. In this article, we show that Phd1 is an unstable protein whose degradation is initiated through phosphorylation by Cdk8 of the RNA polymerase II mediator subcomplex. Phd1 is stabilized by cdk8 disruption, and the naturally filamenting Σ1278b strain was found to have a sequence polymorphism that eliminates a Cdk8 phosphorylation site, which both stabilizes the protein and contributes to enhanced differentiation. In nitrogen-starved cells, PHD1 expression is upregulated and the Phd1 protein becomes stabilized, which causes its accumulation during differentiation. PHD1 expression is partially dependent upon Ste12, which was also previously shown to be destabilized by Cdk8-dependent phosphorylations, but to a significantly smaller extent than Phd1. These observations demonstrate the central role that Cdk8 plays in initiation of differentiation. Cdk8 activity is inhibited in cells shifted to limiting nutrient conditions, and we argue that this effect drives the initiation of differentiation through stabilization of multiple transcription factors, including Phd1, that cause activation of genes necessary for filamentous response.
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| Gene | Phenotype | Experiment Type | Mutant Information | Strain Background | Chemical | Details |
|---|---|---|---|---|---|---|
| SSN3 | protein/peptide accumulation: increased Reporter: Phd1p | classical genetics | null Allele: ssn3-Δ | W303 | Details: steady-state levels increased by 20-fold relative to wild-type | |
| SSN3 | protein/peptide accumulation: increased Reporter: Phd1p | classical genetics | null Allele: ssn3-Δ | W303 | Treatment: cycloheximide treated Details: half-life increased from 10 min. to greater than 45 min. | |
| SSN3 | protein/peptide accumulation: increased Reporter: Phd1p | homozygous diploid | null Allele: ssn3-Δ | Sigma1278b | Treatment: cycloheximide treated Details: estimated half-life increased to about 80 min. | |
| SSN3 | protein/peptide accumulation: increased Reporter: Tec1p | classical genetics | null Allele: ssn3-Δ | W303 | Details: steady-state levels increased by 7-fold relative to wild-type | |
| FLO8 | pseudohyphal growth: increased | homozygous diploid | overexpression | S288C | Details: expression of wt FLO8 allele from sigma1278b results in occasional pseudohyphae, which is further enhanced if polymorphic PHD1 allele (S92F) from sigma1278b is co-expressed |
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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 its 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.
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.
| 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.