A 41 amino acid motif in importin-alpha confers binding to importin-beta and hence transit into the nucleus

EMBO J. 1996 Apr 15;15(8):1810-7.


The complex of importin-alpha and -beta is essential for nuclear protein import. It binds the import substrate in the cytosol, and the resulting trimeric complex moves through the nuclear pores, probably as a single entity. Importin-alpha provides the nuclear localization signal binding site, importin-beta the site of initial docking to the pore. Here we show that the conserved, basic N-terminus of importin-alpha is sufficient for importin-beta binding and essential for protein import. The fusion product of this 41 amino acid domain to a heterologous protein if transported into the nucleus in the same way as full-length importin-alpha itself. Transport is dependent on importin-beta but competed by importin-alpha. As no additional part of importin-alpha is needed for translocation, the movement which drives the import substrate complex into the nucleus appears to be generated between importin-beta and structures of the nuclear pore. The domain that binds to importin-beta appears to confer import only, but not re-export out of the nucleus, suggesting that the return of importin-alpha into the cytoplasm is not a simple reversal of its entry.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Binding Sites / genetics
  • Biological Transport, Active
  • Cell Nucleus / metabolism
  • Consensus Sequence
  • Cytoplasm / metabolism
  • DNA, Complementary / genetics
  • Evolution, Molecular
  • Female
  • Humans
  • In Vitro Techniques
  • Karyopherins
  • Molecular Sequence Data
  • Molecular Structure
  • Nuclear Envelope / metabolism
  • Nuclear Proteins / chemistry
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism*
  • Oocytes / metabolism
  • Protein Binding
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Xenopus


  • DNA, Complementary
  • Karyopherins
  • Nuclear Proteins
  • Recombinant Proteins