title: Ran-dependent signal-mediated nuclear import does not require GTP hydrolysis by Ran.
abstract: Nuclear import of classical nuclear localization sequence-containing proteins involves the assembly of an import complex at the cytoplasmic face of the nuclear pore complex (NPC) followed by movement of this complex through the NPC and release of the import substrate into the nuclear interior. This process has historically been thought to require nucleotide hydrolysis as a source of energy. We found, using hydrolysis-resistant GTP analogs and a mutant Ran unable to hydrolyze GTP, that transport of classical nuclear localization sequence containing substrate through the NPC and release of the substrate into the nucleus did not require hydrolysis of GTP by Ran. In fact, for movement of this type of import substrate into the nuclear interior we did not observe a requirement for hydrolysis of any nucleotide triphosphate. We did, however, find that a pool of free GTP (or its structural equivalent) must be added, probably because the GDP Ran that is added must be converted to GTP Ran during the import process. We found that a requirement for GTP hydrolysis can be restored to an import mixture consisting of recombinant import factors by the addition of RCC1, the Ran guanine nucleotide exchange factor.
authors.affiliation: Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: E D
authors.initials: ED
authors.lastname: Schwoebel
authors.forename: B
authors.initials: B
authors.lastname: Talcott
authors.forename: I
authors.initials: I
authors.lastname: Cushman
authors.forename: M S
authors.initials: MS
authors.lastname: Moore
mesh_terms: D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000187:drug effects / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006868:Hydrolysis; D009685:Nuclear Envelope / Q000378:metabolism; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins; D028901:alpha Karyopherins; D028961:beta Karyopherins; D020931:ran GTP-Binding Protein
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins; D028901:alpha Karyopherins; D028961:beta Karyopherins; C087978:karyopherin alpha 2; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein; D005033:Ethylmaleimide