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Export of importin alpha from the nucleus is mediated by a specific nuclear transport factor.

NLS proteins are transported into the nucleus by the importin alpha/beta heterodimer. Importin alpha binds the NLS, while importin beta mediates translocation through the nuclear pore complex. After translocation, RanGTP, whose predicted concentration is high in the nucleus and low in the cytoplasm, binds importin beta and displaces importin alpha. Importin alpha must then be returned to the cytoplasm, leaving the NLS protein behind. Here, we report that the previously identified CAS protein mediates importin alpha re-export. CAS binds strongly to importin alpha only in the presence of RanGTP, forming an importin alpha/CAS/RanGTP complex. Importin alpha is released from this complex in the cytoplasm by the combined action of RanBP1 and RanGAP1. CAS binds preferentially to NLS-free importin alpha, explaining why import substrates stay in the nucleus.

Pubmed ID: 9323134

Authors

  • Kutay U
  • Bischoff FR
  • Kostka S
  • Kraft R
  • Görlich D

Journal

Cell

Publication Data

September 19, 1997

Associated Grants

None

Mesh Terms

  • Animals
  • Apoptosis
  • Biological Transport
  • Carrier Proteins
  • Cellular Apoptosis Susceptibility Protein
  • Cytoplasm
  • GTP-Binding Proteins
  • HeLa Cells
  • Humans
  • Karyopherins
  • Leucine Zippers
  • Nuclear Envelope
  • Nuclear Proteins
  • Oocytes
  • Protein Binding
  • Proteins
  • Recombinant Proteins
  • Solubility
  • Xenopus
  • ran GTP-Binding Protein