title: Saccharomyces cerevisiae Ub-conjugating enzyme Ubc4 binds the proteasome in the presence of translationally damaged proteins.
abstract: Surveillance mechanisms that monitor protein synthesis can promote rapid elimination of misfolded nascent proteins. We showed that the translation elongation factor eEF1A and the proteasome subunit Rpt1 play a central role in the translocation of nascent-damaged proteins to the proteasome. We show here that multiubiquitinated proteins, and the ubiquitin-conjugating (E2) enzyme Ubc4, are rapidly detected in the proteasome following translational damage. However, Ubc4 levels in the proteasome were reduced significantly in a strain that expressed a mutant Rpt1 subunit. Ubc4 and Ubc5 are functionally redundant E2 enzymes that represent ideal candidates for ubiquitinating damaged nascent proteins because they lack significant substrate specificity, are required for the degradation of bulk, damaged proteins, and contribute to cellular stress-tolerance mechanisms. In agreement with this hypothesis, we determined that ubc4Delta ubc5Delta is exceedingly sensitive to protein translation inhibitors. Collectively, these studies suggest a specific role for Ubc4 and Ubc5 in the degradation of cotranslationally damaged proteins that are targeted to the proteasome.
authors.affiliation: Department of Biochemistry, Rm. 383, SPH/Research Building, Robert Wood Johnson Medical School, 683 Hoes Lane, Piscataway, NJ 08854, USA.
authors.forename: Show-Mei
authors.initials: SM
authors.lastname: Chuang
authors.forename: Kiran
authors.initials: K
authors.lastname: Madura
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D015151:Immunoblotting; D009154:Mutation / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D014176:Protein Biosynthesis; D017510:Protein Folding; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C501306:Ubc4 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C084493:RPT1 protein, S cerevisiae