title: Destabilization of binding to cofactors and SCFMet30 is the rate-limiting regulatory step in degradation of polyubiquitinated Met4.
abstract: The Met4 transcriptional activator of methionine biosynthesis is negatively regulated by the SCFMet30 ubiquitin ligase in response to accumulation of methionine. This mechanism requires polyubiquitination, but not proteolysis. We report that a previously unappreciated mechanism involving growth control regulates Met4. Unless methionine is present in the growth medium, polyubiquitinated Met4 is stabilized in late exponential cultures, correlating with transcriptional repression. Polyubiquitinated Met4 becomes destabilized in a proteasome-dependent manner upon reentry into exponential growth, correlating with transcriptional activation. Met4 stabilization is regulated at the level of SCFMet30 binding and requires transcriptional cofactors. These lock Met4 and SCFMet30 into a tight complex active in ubiquitination but incapable of binding the proteasome. Release of polyubiquitinated Met4 from SCFMet30 is sufficient for degradation, and specific sulfur amino acids can promote the degradation by destabilizing Met4 binding to cofactors and SCFMet30. Thus, destabilization of cofactors and SCFMet30 binding is the rate-limiting regulatory step in Met4 proteolysis.
authors.affiliation: Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104; Department of Biochemistry and Molecular Biology, Louisiana State University Health Science Center, Shreveport, Louisiana 71130.
authors.forename: Srikripa
authors.initials: S
authors.lastname: Chandrasekaran
authors.affiliation: Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104.
authors.forename: Andrew E
authors.initials: AE
authors.lastname: Deffenbaugh
authors.affiliation: Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104.
authors.forename: David A
authors.initials: DA
authors.lastname: Ford
authors.affiliation: LISM-CNRS, Marseille Cedex 20, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Bailly
authors.affiliation: Department of Biochemistry and Molecular Biology, Louisiana State University Health Science Center, Shreveport, Louisiana 71130.
authors.forename: Neal
authors.initials: N
authors.lastname: Mathias
authors.affiliation: Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, Missouri 63104. Electronic address: skowyrad@slu.edu.
authors.forename: Dorota
authors.initials: D
authors.lastname: Skowyra
mesh_terms: D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D003067:Coenzymes / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D044783:F-Box Proteins; D008715:Methionine / Q000378:metabolism; D025821:Polyubiquitin / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D003067:Coenzymes; D044783:F-Box Proteins; C470285:MET30 protein, S cerevisiae; C073675:MET4 protein, S cerevisiae; D011994:Recombinant Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D025821:Polyubiquitin; D008715:Methionine; D043743:Ubiquitin-Protein Ligase Complexes; D003545:Cysteine