title: The nucleoporin Nup98 is a site for GDP/GTP exchange on ran and termination of karyopherin beta 2-mediated nuclear import.
abstract: Karyopherin beta2 (Kapbeta2, transportin) binds the M9 sequence of human ribonucleoprotein A1 and mediates its nuclear import. Here we show a role for the nucleoporin Nup98 in the disassembly of Kapbeta2 import complexes at the nuclear side of the nuclear pore complex (NPC). Kapbeta2 bound to a region at the N terminus of Nup98 that contains an M9-like sequence. The human ribonucleoprotein A1 M9 sequence competed with Nup98 for binding to Kapbeta2, indicating that Nup98 can dissociate Kapbeta2 from its substrate. Binding of Kapbeta2 to Nup98 was inhibited by Ran loaded with guanylyl imidophosphate, suggesting that RanGTP dissociates Kapbeta2 from Nup98. RanGTP is produced from RanGDP through nucleotide exchange mediated by RanGEF (RCC1). Immunoelectron microscopy and nucleotide exchange assays revealed functional RanGEF on both sides of the NPC. On the nuclear side, the localization of RanGEF coincided with that of Nup98. RanGEF bound to Nup98 at a region adjacent to the Kapbeta2-binding site. These findings suggest a model where 1) import substrate is released from Kapbeta2 at the nucleoplasmic side of the NPC by competition with the Nup98 M9-like site, 2) Nup98-bound RanGEF catalyzes the formation of RanGTP, and 3) RanGTP dissociates Kapbeta2 from Nup98 allowing repeated cycles of import.
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute, The Rockefeller University, New York, New York 10021, USA.
authors.forename: B M
authors.initials: BM
authors.lastname: Fontoura
authors.forename: G
authors.initials: G
authors.lastname: Blobel
authors.forename: N R
authors.initials: NR
authors.lastname: Yaseen
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D015723:Gene Library; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D007150:Immunohistochemistry; D028884:Karyopherins; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D020931:ran GTP-Binding Protein / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D020662:Guanine Nucleotide Exchange Factors; D028884:Karyopherins; D008565:Membrane Proteins; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; C093350:nuclear pore complex protein 98; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020931:ran GTP-Binding Protein