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Molecular and Cellular Biology, February 1999, p. 1547-1557, Vol. 19, No. 2
Department of Biological Chemistry and
Molecular Pharmacology, Harvard Medical School, and The Dana-Farber
Cancer Institute, Boston, Massachusetts 02115
Received 12 August 1998/Returned for modification 12 October
1998/Accepted 28 October 1998
Proteins to be transported into the nucleus are recognized by
members of the importin-karyopherin nuclear transport receptor family.
After docking at the nuclear pore complex (NPC), the cargo-receptor complex moves through the aqueous pore channel. Once cargo is released,
the importin then moves back through the channel for new rounds of
transport. Thus, importin and exportin, another member of this family
involved in export, are thought to continuously shuttle between the
nuclear interior and the cytoplasm. In order to understand how nuclear
transporters traverse the NPC, we constructed functional protein
fusions between several members of the yeast importin family, including
Pse1p, Sxm1p, Xpo1p, and Kap95p, and the green fluorescent protein
(GFP). Complexes containing nuclear transporters were isolated by using
highly specific anti-GFP antibodies. Pse1-GFP was studied in the most
detail. Pse1-GFP is in a complex with importin-
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Interactions between a Nuclear Transporter and a
Subset of Nuclear Pore Complex Proteins Depend on Ran GTPase


and -
(Srp1p and
Kap95p in yeast cells) that is sensitive to the nucleotide-bound state
of the Ran GTPase. In addition, Pse1p associates with the nucleoporins
Nsp1p, Nup159p, and Nup116p, while Sxm1p, Xpo1p, and Kap95p show
different patterns of interaction with nucleoporins. Association of
Pse1p with nucleoporins also depends on the nucleotide-bound state of
Ran; when Ran is in the GTP-bound state, the nucleoporin association is
lost. A mutant form of Pse1p that does not bind Ran also fails to
interact with nucleoporins. These data indicate that transport
receptors such as Pse1p interact in a Ran-dependent manner with certain nucleoporins. These nucleoporins may represent major docking sites for
Pse1p as it moves in or out of the nucleus via the NPC.
*
Corresponding author. Mailing address: The Dana-Farber
Cancer Institute, 44 Binney St., Boston, MA 02115. Phone: (617)
632-5102. Fax: (617) 632-5103. E-mail:
pfas.harvard.silver{at}edu.
Present address: ZMBH, Im Neuenheimer Feld 282, D-69120 Heidelberg, Germany.
Present address: Ludwig Institute for Cancer Research, University
of California at San Diego, La Jolla, Calif.
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