Sem1p is a novel subunit of the 26 S proteasome from Saccharomyces cerevisiae.
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.
Mesh Terms:
Blotting, Western, Catalysis, Cell Line, Cysteine Endopeptidases, Electrophoresis, Polyacrylamide Gel, Epitopes, Gene Deletion, Genetic Complementation Test, Glutathione Transferase, Hemagglutinins, Humans, Multienzyme Complexes, Mutation, Peptide Hydrolases, Peptides, Phenotype, Precipitin Tests, Proteasome Endopeptidase Complex, Protein Conformation, Protein Structure, Tertiary, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Salts, Temperature, Time Factors, Transfection, Ubiquitin
Blotting, Western, Catalysis, Cell Line, Cysteine Endopeptidases, Electrophoresis, Polyacrylamide Gel, Epitopes, Gene Deletion, Genetic Complementation Test, Glutathione Transferase, Hemagglutinins, Humans, Multienzyme Complexes, Mutation, Peptide Hydrolases, Peptides, Phenotype, Precipitin Tests, Proteasome Endopeptidase Complex, Protein Conformation, Protein Structure, Tertiary, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Salts, Temperature, Time Factors, Transfection, Ubiquitin
J. Biol. Chem.
Date: Jul. 02, 2004
PubMed ID: 15117943
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