title: Sem1p is a novel subunit of the 26 S proteasome from Saccharomyces cerevisiae.
abstract: The 26 S proteasome, which catalyzes degradation of polyubiquitinated proteins, is composed of the 20 S proteasome and the 19 S regulatory particle (RP). The RP is composed of the lid and base subcomplexes and regulates the catalytic activity of the 20 S proteasome. In this study, we carried out affinity purification of the lid and base subcomplexes from the tagged strains of Saccharomyces cerevisiae, and we found that the lid contains a small molecular mass protein, Sem1. The Sem1 protein binds with the 26 S proteasome isolated from a mutant with deletion of SEM1 but not with the 26 S proteasome from the wild type. The lid lacking Sem1 is unstable at a high salt concentration. The 19 S RP was immunoprecipitated together with Sem1 by immunoprecipitation using hemagglutinin epitope-tagged Sem1 as bait. Degradation of polyubiquitinated proteins in vivo or in vitro is impaired in the Sem1-deficient 26 S proteasome. In addition, genetic interaction between SEM1 and RPN10 was detected. The human Sem1 homologue hDSS1 was found to be a functional homologue of Sem1 and capable of interacting with the human 26 S proteasome. The results suggest that Sem1, possibly hDSS1, is a novel subunit of the 26 S proteasome and plays a role in ubiquitin-dependent proteolysis.
authors.affiliation: Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Sone
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Saeki
authors.forename: Akio
authors.initials: A
authors.lastname: Toh-e
authors.forename: Hideyoshi
authors.initials: H
authors.lastname: Yokosawa
mesh_terms: D015153:Blotting, Western; D002384:Catalysis; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes / Q000737:chemistry; D017353:Gene Deletion; D005816:Genetic Complementation Test; D005982:Glutathione Transferase / Q000378:metabolism; D006388:Hemagglutinins / Q000737:chemistry; D006801:Humans; D009097:Multienzyme Complexes / Q000378:metabolism; D009154:Mutation; D010447:Peptide Hydrolases / Q000737:chemistry / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry; D010641:Phenotype; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000378:metabolism; D012492:Salts / Q000494:pharmacology; D013696:Temperature; D013997:Time Factors; D014162:Transfection; D025801:Ubiquitin / Q000737:chemistry
chemical_list: D000939:Epitopes; D006388:Hemagglutinins; D009097:Multienzyme Complexes; D010455:Peptides; C117424:SEM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D012492:Salts; D025801:Ubiquitin; D005982:Glutathione Transferase; D010447:Peptide Hydrolases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease