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RanBP1 stabilizes the interaction of Ran with p97 nuclear protein import.

Three factors have been identified that reconstitute nuclear protein import in a permeabilized cell assay: the NLS receptor, p97, and Ran/TC4. Ran/TC4, in turn, interacts with a number of proteins that are involved in the regulation of GTP hydrolysis or are components of the nuclear pore. Two Ran-binding proteins, RanBP1 and RanBP2, form discrete complexes with p97 as demonstrated by immunoadsorption from HeLa cell extracts fractionated by gel filtration chromatography. A > 400-kD complex contains p97, Ran, and RanBP2. Another complex of 150-300 kD was comprised of p97, Ran, and RanBP1. This second trimeric complex could be reconstituted from recombinant proteins. In solution binding assays, Ran-GTP bound p97 with high affinity, but the binding of Ran-GDP to p97 was undetectable. The addition of RanBP1 with Ran-GDP or Ran-GTP increased the affinity of both forms of Ran for p97 to the same level. Binding of Ran-GTP to p97 dissociated p97 from immobilized NLS receptor while the Ran-GDP/RanBP1/p97 complex did not dissociate from the receptor. In a digitonin-permeabilized cell docking assay, RanBP1 stabilizes the receptor complex against temperature-dependent release from the pore. When added to an import assay with recombinant NLS receptor, p97 and Ran-GDP, RanBP1 significantly stimulates transport. These results suggest that RanBP1 promotes both the docking and translocation steps in nuclear protein import by stabilizing the interaction of Ran-GDP with p97.

Pubmed ID: 8909533


  • Chi NC
  • Adam EJ
  • Visser GD
  • Adam SA


The Journal of cell biology

Publication Data

November 16, 1996

Associated Grants

  • Agency: NCI NIH HHS, Id: 5-T32 CA 09560
  • Agency: NIGMS NIH HHS, Id: 5-T32-GM08152-10
  • Agency: NIGMS NIH HHS, Id: GM 47866

Mesh Terms

  • Biological Transport
  • Cell Membrane Permeability
  • Cell Nucleus
  • DNA-Binding Proteins
  • Digitonin
  • GTP-Binding Proteins
  • Guanosine Diphosphate
  • Guanosine Triphosphate
  • HeLa Cells
  • Humans
  • Macromolecular Substances
  • Molecular Chaperones
  • Nuclear Envelope
  • Nuclear Pore Complex Proteins
  • Nuclear Proteins
  • Protein Binding
  • Recombinant Fusion Proteins
  • alpha Karyopherins
  • beta Karyopherins
  • ran GTP-Binding Protein