Sem1p Is a Novel Subunit of the 26 S Proteasome from Saccharomyces cerevisiae

• Published in: The Journal of biological chemistry Vol. 279; no. 27; pp. 28807 - 28816
• Main Authors: Sone, Takayuki, Saeki, Yasushi, Toh-e, Akio, Yokosawa, Hideyoshi
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 02.07.2004
• Subjects: Blotting, Western; Catalysis; Cell Line; Cysteine Endopeptidases - metabolism; Electrophoresis, Polyacrylamide Gel; Epitopes - chemistry; Gene Deletion; Genetic Complementation Test; Glutathione Transferase - metabolism; Hemagglutinins - chemistry; Humans; Multienzyme Complexes - metabolism; Mutation; Peptide Hydrolases - chemistry; Peptide Hydrolases - metabolism; Peptides - chemistry; Phenotype; Precipitin Tests; Proteasome Endopeptidase Complex; Protein Conformation; Protein Structure, Tertiary; Saccharomyces cerevisiae; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - chemistry; Saccharomyces cerevisiae Proteins - metabolism; Salts - pharmacology; Temperature; Time Factors; Transfection; Ubiquitin - chemistry
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M403165200

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.