title: SCFCdc4-mediated degradation of the Hac1p transcription factor regulates the unfolded protein response in Saccharomyces cerevisiae.
abstract: The Saccharomyces cerevisiae basic leucine zipper transcription factor Hac1p is synthesized in response to the accumulation of unfolded polypeptides in the lumen of the endoplasmic reticulum (ER), and it is responsible for up-regulation of approximately 5% of all yeast genes, including ER-resident chaperones and protein-folding catalysts. Hac1p is one of the most short-lived yeast proteins, having a half-life of approximately 1.5 min. Here, we have shown that Hac1p harbors a functional PEST degron and that degradation of Hac1p by the proteasome involves the E2 ubiquitin-conjugating enzyme Ubc3/Cdc34p and the SCF(Cdc4) E3 complex. Consistent with the known nuclear localization of Cdc4p, rapid degradation of Hac1p requires the presence of a functional nuclear localization sequence, which we demonstrated to involve basic residues in the sequence (29)RKRAKTK(35). Two-hybrid analysis demonstrated that the PEST-dependent interaction of Hac1p with Cdc4p requires Ser146 and Ser149. Turnover of Hac1p may be dependent on transcription because it is inhibited in cell mutants lacking Srb10 kinase, a component of the SRB/mediator module of the RNA polymerase II holoenzyme. Stabilization of Hac1p by point mutation or deletion, or as the consequence of defects in components of the degradation pathway, results in increased unfolded protein response element-dependent transcription and improved cell viability under ER stress conditions.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Melbourne, Victoria 3010, Australia.
authors.forename: Bhupinder
authors.initials: B
authors.lastname: Pal
authors.forename: Nickie C
authors.initials: NC
authors.lastname: Chan
authors.forename: Leon
authors.initials: L
authors.lastname: Helfenbaum
authors.forename: Kaeling
authors.initials: K
authors.lastname: Tan
authors.forename: William P
authors.initials: WP
authors.lastname: Tansey
authors.forename: Mary-Jane
authors.initials: MJ
authors.lastname: Gething
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D064173:Anaphase-Promoting Complex-Cyclosome; D050976:Basic-Leucine Zipper Transcription Factors / Q000032:analysis / Q000378:metabolism*; D001665:Binding Sites; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000737:chemistry / Q000378:metabolism; D002470:Cell Survival; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D044783:F-Box Proteins; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D017510:Protein Folding; D012097:Repressor Proteins / Q000032:analysis / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000032:analysis / Q000378:metabolism*; D012694:Serine / Q000737:chemistry / Q000235:genetics; D014157:Transcription Factors / Q000032:analysis / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; C080443:CDC4 protein, S cerevisiae; D018797:Cell Cycle Proteins; D044783:F-Box Proteins; C091341:HAC1 protein, S cerevisiae; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D025801:Ubiquitin; D012694:Serine; C577449:CDC34 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D044767:Ubiquitin-Protein Ligases; D056850:Cyclin-Dependent Kinase 8; D018844:Cyclin-Dependent Kinases; C498309:SSN3 protein, S cerevisiae; D020929:Mitogen-Activated Protein Kinase Kinases; D046988:Proteasome Endopeptidase Complex