title: Autophosphorylation-induced degradation of the Pho85 cyclin Pcl5 is essential for response to amino acid limitation.
abstract: Pho85 cyclins (Pcls), activators of the yeast cyclin-dependent kinase (CDK) Pho85, belong together with the p35 activator of mammalian CDK5 to a distinct structural cyclin class. Different Pcls target Pho85 to distinct substrates. Pcl5 targets Pho85 specifically to Gcn4, a yeast transcription factor involved in the response to amino acid starvation, eventually causing the degradation of Gcn4. Pcl5 is itself highly unstable, an instability that was postulated to be important for regulation of Gcn4 degradation. We used hybrids between different Pcls to circumscribe the substrate recognition function to the core cyclin box domain of Pcl5. Furthermore, the cyclin hybrids revealed that Pcl5 degradation is uniquely dependent on two distinct degradation signals: one N-terminal and one C-terminal to the cyclin box domain. Whereas the C-terminal degradation signal is independent of Pho85, the N-terminal degradation signal requires phosphorylation of a specific threonine residue by the Pho85 molecule bound to the cyclin. This latter mode of degradation depends on the SCF ubiquitin ligase. Degradation of Pcl5 after self-catalyzed phosphorylation ensures that activity of the Pho85/Pcl5 complex is self-limiting in vivo. We demonstrate the importance of this mechanism for the regulation of Gcn4 degradation and for cell growth under conditions of amino acid starvation.
authors.affiliation: Department of Molecular Microbiology, B. Rappaport Faculty of Medicine, Technion-I.I.T., 2 Efron St., Haifa 31096, Israel.
authors.forename: Sharon
authors.initials: S
authors.lastname: Aviram
authors.forename: Einav
authors.initials: E
authors.lastname: Simon
authors.forename: Tsvia
authors.initials: T
authors.lastname: Gildor
authors.forename: Fabian
authors.initials: F
authors.lastname: Glaser
authors.forename: Daniel
authors.initials: D
authors.lastname: Kornitzer
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D050976:Basic-Leucine Zipper Transcription Factors; D018844:Cyclin-Dependent Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010766:Phosphorylation; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D013379:Substrate Specificity; D013912:Threonine / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D000596:Amino Acids; D050976:Basic-Leucine Zipper Transcription Factors; D016213:Cyclins; D004268:DNA-Binding Proteins; C501391:GCN4 protein, S cerevisiae; C461492:PCL5 protein, S cerevisiae; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D013912:Threonine; D044843:SKP Cullin F-Box Protein Ligases; D018844:Cyclin-Dependent Kinases; C058605:PHO85 protein, S cerevisiae
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