Dynamic localization of the nuclear import receptor and its interactions with transport factors.
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.
Koepp
D M
DM
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
Wong
D H
DH
Corbett
A H
AH
Silver
P A
PA
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
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