title: The yeast nucleoporin Nup2p is involved in nuclear export of importin alpha/Srp1p.
abstract: The importin alpha.beta 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 alpha 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 in Deltanup2 mutants. Also, Srp1p fusion proteins accumulate at the nuclear rim in wild-type cells but accumulate in the nuclear interior in Deltanup2 cells. A deletion of NUP2 shows genetic interactions with mutants in SRP1 and PRP20, 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.
authors.affiliation: W.M. Keck Institute for Cellular Visualization, Department of Biology, Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: J W
authors.initials: JW
authors.lastname: Booth
authors.forename: K D
authors.initials: KD
authors.lastname: Belanger
authors.forename: M I
authors.initials: MI
authors.lastname: Sannella
authors.forename: L I
authors.initials: LI
authors.lastname: Davis
mesh_terms: D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active; D002467:Cell Nucleus / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D008565:Membrane Proteins / Q000378:metabolism; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D018272:Porins / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D029701:Saccharomyces cerevisiae Proteins; D015003:Yeasts; D028901:alpha Karyopherins
chemical_list: D008565:Membrane Proteins; C064550:NUP1 protein, S cerevisiae; C400753:NUP2 protein, S cerevisiae; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D018272:Porins; D029701:Saccharomyces cerevisiae Proteins; D028901:alpha Karyopherins