title: Dynamic localization of the nuclear import receptor and its interactions with transport factors.
abstract: Characterization of the interactions between soluble factors required for nuclear transport is key to understanding the process of nuclear trafficking. Using a synthetic lethal screen with the rna1-1 strain, we have identified a genetic interaction between Rna1p, a GTPase activating protein required for nuclear transport, and yeast importin-beta, a component of the nuclear localization signal receptor. By the use of fusion proteins, we demonstrate that Rna1p physically interacts with importin-beta. Mutants in importin-beta exhibit in vivo nuclear protein import defects, and importin-beta localizes to the nuclear envelope along with other proteins associated with the nuclear pore complex. In addition, we present evidence that importin-alpha, but not importin-beta, mislocalizes to the nucleus in cells where the GTPase Ran is likely to be in the GDP-bound state. We suggest a model of nuclear transport in which Ran-mediated hydrolysis of GTP is necessary for the import of importin-alpha and the nuclear localization signal-bearing substrate into the nucleus, while exchange of GDP for GTP on Ran is required for the export of both mRNA and importin-alpha from the nucleus.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Koepp
authors.forename: D H
authors.initials: DH
authors.lastname: Wong
authors.forename: A H
authors.initials: AH
authors.lastname: Corbett
authors.forename: P A
authors.initials: PA
authors.lastname: Silver
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001692:Biological Transport; D002467:Cell Nucleus / Q000737:chemistry; D004268:DNA-Binding Proteins; D005656:Fungal Proteins / Q000032:analysis / Q000378:metabolism* / Q000502:physiology; D020690:GTPase-Activating Proteins; D005800:Genes, Fungal / Q000235:genetics; D005804:Genes, Lethal; D005816:Genetic Complementation Test; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism; D028884:Karyopherins; D008969:Molecular Sequence Data; D009154:Mutation; D009685:Nuclear Envelope / Q000737:chemistry*; D009687:Nuclear Proteins / Q000032:analysis* / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D011485:Protein Binding; D012333:RNA, Messenger / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D015003:Yeasts / Q000166:cytology / Q000235:genetics; D020931:ran GTP-Binding Protein
chemical_list: D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D028884:Karyopherins; D009687:Nuclear Proteins; D012333:RNA, Messenger; C060997:RNA1 protein, S cerevisiae; D011993:Recombinant Fusion Proteins; C067050:SRM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein