The Yeast Nucleoporin Nup2p Is Involved in Nuclear Export of Importin α/Srp1p*
- From the ‡W. M. Keck Institute for Cellular Visualization, Rosenstiel Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02454 and the ¶Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710
Abstract
The importin α·β heterodimer mediates nuclear import of proteins containing classical nuclear localization signals. After carrying its cargo into the nucleus, the importin dimer dissociates, and Srp1p (the yeast importin α subunit) is recycled to the cytoplasm in a complex with Cse1p and RanGTP. Nup2p is a yeast FXFG nucleoporin that contains a Ran-binding domain. We find that export of Srp1p from the nucleus is impaired inΔnup2 mutants. Also, Srp1p fusion proteins accumulate at the nuclear rim in wild-type cells but accumulate in the nuclear interior in Δnup2 cells. A deletion of NUP2shows genetic interactions with mutants in SRP1 andPRP20, which encodes the Ran nucleotide exchange factor. Srp1p binds directly to an N-terminal domain of Nup2p. This region of Nup2p is sufficient to allow accumulation of an Srp1p fusion protein at the nuclear rim, but the C-terminal Ran-binding domain of Nup2p is required for efficient Srp1p export. Formation of the Srp1p·Cse1p·RanGTP export complex releases Srp1p from its binding site in Nup2p. We propose that Nup2p may act as a scaffold that facilitates formation of the Srp1p export complex.
Footnotes
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↵* This work was supported by National Institutes of Health Grant GM-54768-04 (to L. I. D.) and by a Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada (to J. W. B.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Present address: Division of Cell Biology, The Hospital for Sick Children, 555 University Ave., Toronto, Ontario M5G 1X8, Canada.
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↵‖ Present address: Dept. of Biology, 106 Loyola Hall, University of Scranton, Scranton, PA 18510.
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↵** To whom correspondence should be addressed: Rosenstiel Center, MS 029, Brandeis University, 415 South St., Waltham, MA 02454. Tel.: 781-736-2451; Fax: 781-736-2405; E-mail: davis@hydra.rose.brandeis.edu.
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↵2 J. A. Hoffman and L. I. Davis, unpublished data.
- Abbreviations:
- NPC
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nuclear pore complex
- NLS
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nuclear localization signal
- RanBD
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Ran-binding domain
- GST
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glutathione S-transferase
- GFP
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green fluorescent protein
- PAGE
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polyacrylamide gel electrophoresis
- DAPI
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4′,6-diamidino-2-phenylindole
- HSA
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human serum albumin
- mAb
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monoclonal antibody
- PCR
-
polymerase chain reaction
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- Received June 23, 1999.
- Revision received August 18, 1999.
- The American Society for Biochemistry and Molecular Biology, Inc.
