title: 20 S proteasomes are imported as precursor complexes into the nucleus of yeast.
abstract: The mechanism by which yeast 20 S proteasomes are imported into the nucleus is still unresolved. Here, we provide the first evidence that 20 S proteasomes are imported as precursor complexes into the nucleus. By using the srp1-49 mutant which is deficient in nuclear import of cargos with classical nuclear localization sequences (cNLS), we show that proteasome precursor complexes associate with importin/karyopherin alphabeta, the cNLS receptor, and that they accumulate inside the cytoplasm. Reconstitution assays revealed that only precursor complexes are targeted to the nuclear envelope (NE) by karyopherin alphabeta. In support, the green fluorescent protein (GFP)-labelled maturation factor Ump1, marking precursor complexes, mainly localizes to the nucleus and around the NE. Our data suggest that nuclear 20 S proteasomes are finally matured inside the nucleus.
authors.affiliation: Institut für Biochemie, Humboldt Universität zu Berlin, Universitätsklinikum Charité, Monbijoustr. 2, Berlin, D-10117, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Lehmann
authors.forename: Katharina
authors.initials: K
authors.lastname: Janek
authors.forename: Beate
authors.initials: B
authors.lastname: Braun
authors.forename: Peter-Michael
authors.initials: PM
authors.lastname: Kloetzel
authors.forename: Cordula
authors.initials: C
authors.lastname: Enenkel
mesh_terms: D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000201:enzymology / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D003593:Cytoplasm / Q000201:enzymology / Q000378:metabolism; D018870:Endoplasmic Reticulum, Rough / Q000201:enzymology / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D028884:Karyopherins / Q000378:metabolism; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation; D010449:Peptide Mapping; D046988:Proteasome Endopeptidase Complex; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D012996:Solutions; D014461:Ultracentrifugation
chemical_list: D005656:Fungal Proteins; D006360:Heat-Shock Proteins; D028884:Karyopherins; D009097:Multienzyme Complexes; D011498:Protein Precursors; D029701:Saccharomyces cerevisiae Proteins; D012996:Solutions; C491115:TIR1 protein, S cerevisiae; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex