title: Ran binding domains promote the interaction of Ran with p97/beta-karyopherin, linking the docking and translocation steps of nuclear import.
abstract: Nuclear protein import is accomplished by two sequential events; docking at the nuclear pore complex followed by ATP-dependent translocation across the nuclear envelope. Docking of nuclear targeted proteins requires a 56-kDa nuclear localization signal receptor (alpha-karyopherin, importin-alpha, SRP1 alpha) and a 97-kDa protein (beta-karyopherin, importin-beta). Components necessary for translocation include the Ran/TC4 GTPase and NTF2/B-2. The functions of these factors at a molecular level remain unclear. We have now found that a complex of Ran, in the GTP-bound state, with either the Ran binding protein, RanBP1, or an isolated Ran binding domain binds with high affinity and specificity to beta-karyopherin to form a ternary complex. We find that a C-terminal truncation mutant of Ran, delta-DE Ran, also binds to beta-karyopherin and that delta-DE Ran can associate with a cytosolic, multiprotein complex that contains beta-karyopherin and another delta-DE Ran binding protein of 115/120 kDa. These data suggest a physical link between docking and translocation mediated by a Ran GTPase-Ran binding protein complex.
authors.affiliation: Department of Pathology and Comprehensive Cancer Center, University of Vermont, Burlington 05405, USA. klounsbu@moose.uvm.edu
authors.forename: K M
authors.initials: KM
authors.lastname: Lounsbury
authors.forename: S A
authors.initials: SA
authors.lastname: Richards
authors.forename: R R
authors.initials: RR
authors.lastname: Perlungher
authors.forename: I G
authors.initials: IG
authors.lastname: Macara
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D006224:Cricetinae; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D051381:Rats; D028961:beta Karyopherins; D020931:ran GTP-Binding Protein
chemical_list: D009687:Nuclear Proteins; D028961:beta Karyopherins; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein