title: Rpn5 is a conserved proteasome subunit and required for proper proteasome localization and assembly.
abstract: Proper function of the 26 S proteasome requires assembly of the regulatory complex, which is composed of the lid and base subcomplexes. We characterized Rpn5, a lid subunit, in fission yeast. We show that Rpn5 associates with the proteasome rpn5. Deletion (rpn5Delta) exacerbates the growth defects in proteasome mutants, leading to mitotic abnormalities, which correlate with accumulation of polyubiquitinated proteins, such as Cut2/securin. Rpn5 expression is tightly controlled; both overexpression and deletion of rpn5 impair proteasome functions. The proteasome is assembled around the inner nuclear membrane in wild-type cells; however, in rpn5Delta cells, proteasome subunits are improperly assembled and/or localized. In the lid mutants, Rpn5 is mislocalized in the cytosol, while in the base mutants, Rpn5 can enter the nucleus, but is left in the nucleoplasm, and not assembled into the nuclear membrane. These results suggest that Rpn5 is a dosage-dependent proteasome regulator and plays a role in mediating proper proteasome assembly. Moreover, the Rpn5 assembly may be a cooperative process that involves at least two steps: 1) nuclear import and 2) subsequent assembly into the nuclear membrane. The former step requires other components of the lid, while the latter requires the base. Human Rpn5 rescues the phenotypes associated with rpn5Delta and is incorporated into the yeast proteasome, suggesting that Rpn5 functions are highly conserved.
authors.affiliation: Department of Molecular and Cellular Biology, The Breast Center, Baylor College of Medicine, Methodist Hospital, Houston, Texas 77030, USA.
authors.forename: Hsueh-Chi S
authors.initials: HC
authors.lastname: Yen
authors.forename: Christine
authors.initials: C
authors.lastname: Espiritu
authors.forename: Eric C
authors.initials: EC
authors.lastname: Chang
mesh_terms: D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D020090:Chromosome Segregation; D015825:Chromosomes, Fungal; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D019143:Evolution, Molecular; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D006801:Humans; D020014:K562 Cells; D009097:Multienzyme Complexes / Q000378:metabolism*; D016296:Mutagenesis; D010641:Phenotype; D046988:Proteasome Endopeptidase Complex; D021122:Protein Subunits / Q000235:genetics* / Q000378:metabolism*; D012568:Schizosaccharomyces / Q000235:genetics* / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics* / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D009097:Multienzyme Complexes; D021122:Protein Subunits; D029702:Schizosaccharomyces pombe Proteins; C471107:rpn501 protein, S pombe; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex