title: Sem1, the yeast ortholog of a human BRCA2-binding protein, is a component of the proteasome regulatory particle that enhances proteasome stability.
abstract: Degradation of polyubiquitinated proteins by the proteasome often requires accessory factors; these include receptor proteins that bind both polyubiquitin chains and the regulatory particle of the proteasome. Overproduction of one such factor, Dsk2, is lethal in Saccharomyces cerevisiae and we show here that this lethality can be suppressed by mutations in SEM1, a gene previously recognized as an ortholog of the human gene encoding DSS1, which binds the BRCA2 DNA repair protein. Yeast sem1 mutants accumulate polyubiquitinated proteins, are defective for proteasome-mediated degradation and cannot grow under various stress conditions. Moreover, sem1 is synthetically lethal with mutations in proteasome subunits. We show that Sem1 is a component of the regulatory particle of the proteasome, specifically the lid subcomplex. Loss of Sem1 impairs the stability of the 26S proteasome and sem1Delta defects are greatly enhanced by simultaneous deletion of RPN10. The Rpn10 proteasome subunit appears to function with Sem1 in maintaining the association of the lid and base subcomplexes of the regulatory particle. Our data suggest a potential mechanism for this protein-protein stabilization and also suggest that an intact proteasomal regulatory particle is required for responses to DNA damage.
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Sciences, Kyushu University, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Funakoshi
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.forename: Irina
authors.initials: I
authors.lastname: Velichutina
authors.forename: Mark
authors.initials: M
authors.lastname: Hochstrasser
authors.forename: Hideki
authors.initials: H
authors.lastname: Kobayashi
mesh_terms: D024682:BRCA2 Protein / Q000235:genetics*; D005656:Fungal Proteins / Q000737:chemistry* / Q000378:metabolism; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D005804:Genes, Lethal; D006801:Humans; D015151:Immunoblotting; D017354:Point Mutation; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D024682:BRCA2 Protein; D005656:Fungal Proteins; C117424:SEM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex