title: Cdk8 regulates stability of the transcription factor Phd1 to control pseudohyphal differentiation of Saccharomyces cerevisiae.
abstract: 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.
authors: Department of Biochemistry and Molecular Biology, Molecular Epigenetics, LSI, University of British Columbia, Vancouver, British Columbia, Canada.
authors: Sheetal
authors: S
authors: Raithatha
authors: Ting-Cheng
authors: TC
authors: Su
authors: Pedro
authors: P
authors: Lourenco
authors: Susan
authors: S
authors: Goto
authors: Ivan
authors: I
authors: Sadowski
mesh_terms: D056850:Cyclin-Dependent Kinase 8 / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D011110:Polymorphism, Genetic; D055550:Protein Stability; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; C085984:PHD1 protein, S cerevisiae; C489241:STE12 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D056850:Cyclin-Dependent Kinase 8; C498309:SSN3 protein, S cerevisiae; D012319:RNA Polymerase II