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Original Article |
Correspondence to: David S. Goldfarb, Department of Biology, University of Rochester, Rochester, NY 14627. Tel:(716) 275-3890 Fax:(716) 275-2070 E-mail:dasg{at}mail.rochester.edu.
The vertebrate nuclear pore complex (NPC) harbors an ~10-nm diameter diffusion channel that is large enough to admit 50-kD polypeptides. We have analyzed the permeability properties of the Saccharomyces cerevisiae nuclear envelope (NE) using import (NLS) and export (NES) signal-containing green fluorescent protein (GFP) reporters. Compared with wild-type, passive export rates of a classical karyopherin/importin (Kap) Kap60p/Kap95p-targeted NLS-GFP reporter (cNLS-GFP) were significantly faster in nup188-
and nup170-
cells. Similar results were obtained using two other NLS-GFP reporters, containing either the Kap104p-targeted Nab2p NLS (rgNLS) or the Kap121p-targeted Pho4p NLS (pNLS). Elevated levels of Hsp70 stimulated cNLS-GFP import, but had no effect on the import of rgNLS-GFP. Thus, the role of Hsp70 in NLS-directed import may be NLS- or targeting pathway-specific. Equilibrium sieving limits for the diffusion channel were assessed in vivo using NES-GFP reporters of 36126 kD and were found to be greater than wild-type in nup188-
and nup170-
cells. We propose that Nup170p and Nup188p are involved in establishing the functional resting diameter of the NPC's central transport channel.
Key Words: nuclear pore complex, import/export signals, green fluorescent protein, diffusion channel, Saccharomyces cerevisiae
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