A novel receptor-mediated nuclear protein import pathway

Cell. 1996 Sep 20;86(6):985-94. doi: 10.1016/s0092-8674(00)80173-7.


Targeting of most nuclear proteins to the cell nucleus is initiated by interaction between the classical nuclear localization signals (NLSs) contained within them and the importin NLS receptor complex. We have recently delineated a novel 38 amino acid transport signal in the hnRNP A1 protein, termed M9, which confers bidirectional transport across the nuclear envelope. We show here that M9-mediated nuclear import occurs by a novel pathway that is independent of the well-characterized, importin-mediated classical NLS pathway. Additionally, we have identified a specific M9-interacting protein, termed transportin, which binds to wild-type M9 but not to transport-defective M9 mutants. Transportin is a 90 kDa protein, distantly related to importin beta, and we show that it mediates the nuclear import of M9-containing proteins. These findings demonstrate that there are at least two receptor-mediated nuclear protein import pathways. Furthermore, as hnRNP A1 likely participates in mRNA export, it raises the possibility that transportin is a mediator of this process as well.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Biological Transport, Active
  • HeLa Cells
  • Heterogeneous Nuclear Ribonucleoprotein A1
  • Heterogeneous-Nuclear Ribonucleoprotein Group A-B*
  • Heterogeneous-Nuclear Ribonucleoproteins
  • Humans
  • In Vitro Techniques
  • Molecular Sequence Data
  • Mutation
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism*
  • Protein Sorting Signals / genetics
  • Protein Sorting Signals / metabolism
  • RNA, Messenger / metabolism
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Ribonucleoproteins / genetics
  • Ribonucleoproteins / metabolism
  • Sequence Homology, Amino Acid
  • beta Karyopherins


  • Heterogeneous Nuclear Ribonucleoprotein A1
  • Heterogeneous-Nuclear Ribonucleoprotein Group A-B
  • Heterogeneous-Nuclear Ribonucleoproteins
  • Nuclear Proteins
  • Protein Sorting Signals
  • RNA, Messenger
  • Receptors, Cytoplasmic and Nuclear
  • Recombinant Proteins
  • Ribonucleoproteins
  • beta Karyopherins

Associated data

  • GENBANK/U70322