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Original Article |
Correspondence to: Mary Shannon Moore, Baylor College of Medicine, Department of Molecular and Cellular Biology, One Baylor Plaza, Houston, TX 77030. Tel:(713) 798-6656 Fax:(713) 798-7799
p10/NTF2 is a nuclear transport carrier that mediates the uptake of cytoplasmic RanGDP into the nucleus. We constructed a point mutant of p10, D23A, that exhibited unexpected behavior both in digitonin-permeabilized and microinjected mammalian cells. D23A p10 was markedly more efficient than wild-type (wt) p10 at supporting Ran import, but simultaneously acted as a dominant-negative inhibitor of classical nuclear localization sequence (cNLS)-mediated nuclear import supported by karyopherins (Kaps) 
and ß1. Binding studies indicated that these two nuclear transport carriers of different classes, p10 and Kap-ß1, compete for identical and/or overlapping binding sites at the nuclear pore complex (NPC) and that D23A p10 has an increased affinity relative to wt p10 and Kap-ß1 for these shared binding sites. Because of this increased affinity, D23A p10 is able to import its own cargo (RanGDP) more efficiently than wt p10, but Kap-ß1 can no longer compete efficiently for shared NPC docking sites, thus the import of cNLS cargo is inhibited. The competition of different nuclear carriers for shared NPC docking sites observed here predicts a dynamic equilibrium between multiple nuclear transport pathways inside the cell that could be easily shifted by a transient modification of one of the carriers.
Key Words: nuclear transport, nuclear pore complex, p10, NTF2, karyopherin
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