title: Import and export of the nuclear protein import receptor transportin by a mechanism independent of GTP hydrolysis.
abstract: BACKGROUND
  Nuclear protein import and export are mediated by receptor proteins that recognize nuclear localization sequences (NLSs) or nuclear export sequences (NESs) and target the NLS-bearing or NES-bearing protein to the nuclear pore complex (NPC). Temperature-dependent translocation of the receptor-cargo complex in both directions through the NPC requires the GTPase Ran, and it has been proposed that the Ran GTPase cycle mediates translocation. We have addressed the role of GTP hydrolysis in these processes by studying the import receptor transportin, which mediates the import of a group of abundant heterogeneous nuclear RNA-binding proteins bearing the M9 NLS.
  
  
  RESULTS
  We investigated the transport properties of transportin and found that the carboxy-terminal region of transportin could, by itself, be imported into the nucleus. Transportin import and export were inhibited by low temperature in vitro, but were unaffected by the non-hydrolyzable GTP analogue GMP-PNP.
  
  
  CONCLUSIONS
  Temperature-dependent import and export through the NPC can be uncoupled from the Ran GTPase cycle and can occur without GTP hydrolysis.
authors.affiliation: Howard Hughes Medical Institute, Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6148, USA.
authors.forename: S
authors.initials: S
authors.lastname: Nakielny
authors.forename: G
authors.initials: G
authors.lastname: Dreyfuss
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D006868:Hydrolysis; D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013696:Temperature
chemical_list: D028884:Karyopherins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate