Qualitative highly divergent nuclear export signals can regulate export by the competition for transport cofactors in vivo.
Nucleo-cytoplasmic transport of proteins is mediated by nuclear export signals, identified in various proteins executing heterologous biological functions. However, the molecular mechanism underlying the orchestration of export is only poorly understood. Using microinjection of defined recombinant export substrates, we now demonstrate that leucine-rich nuclear export signals varied dramatically in determining the kinetics of export in vivo. Thus, nuclear export signals could be kinetically classified which correlated with their affinities for CRM1-containing export complexes in vitro. Strikingly, cotransfection experiments revealed that proteins containing a fast nuclear export signal inhibited export and the biological activity of proteins harboring a slower nuclear export signal in vivo. The affinity for export complexes seems therefore predominantly controlled by the nuclear export signal itself, even in the context of the complete protein in vivo. Overexpression of FG-rich repeats of nucleoporins affected a medium nuclear export signal containing protein to the same extent as a fast nuclear export signal containing protein, indicating that nucleoporins appear not to contribute significantly to nuclear export signal-specific export regulation. Our results imply a novel mode for controlling the biological activity of shuttle proteins already by the composition of the nuclear export signal itself.
Heger
P
P
Institute for Clinical and Molecular Virology, University of Erlangen-Nürnberg, Schlossgarten 4, D-91054 Erlangen, Germany.
Lohmaier
J
J
Schneider
G
G
Schweimer
K
K
Stauber
R H
RH
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D015694:Gene Products, rev / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins; D007700:Kinetics; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D015533:Transcriptional Activation; D014709:Vero Cells; D014981:Xenopus; D000097606:Exportin 1 Protein
D002352:Carrier Proteins; D015500:Chloramphenicol O-Acetyltransferase; D015694:Gene Products, rev; D005982:Glutathione Transferase; D028884:Karyopherins; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D000097606:Exportin 1 Protein