title: The Ran/TC4 GTPase-binding domain: identification by expression cloning and characterization of a conserved sequence motif.
abstract: Ran/TC4 is an essential, nuclear GTPase implicated in the initiation of DNA replication, entry into and exit from mitosis, and in nuclear RNA and protein transport through the nuclear pore complex. This diversity of functions suggests that Ran interacts with a large number of down-stream targets. Using an overlay assay, we detected a family of putative target proteins that associate with GTP-bound Ran. The sequence of only one such protein, HTF9a/RanBP1, is known. We have now cloned two additional Ran-binding proteins, allowing identification of a distinctive, highly conserved sequence motif of approximately 150 residues. This motif represents a minimal Ran-binding domain that stabilizes the GTP-bound state of Ran. The isolated domain also functions as a coactivator of Ran-GTPase-activating protein. Mutation of a conserved residue within the Ran-binding domain of HTF9a protein drastically reduced Ran binding. Ran-binding proteins coimmunoprecipitated with epitope-tagged Ran from cell lysates, suggesting that these proteins may associate in vivo. A previously uncharacterized Caenorhabditis elegans gene could encode a protein (96 kDa) possessing two Ran-binding domains. This open reading frame also contains similarities to nucleoporins, suggesting a functional link between Ran and nuclear pore complexes.
authors.affiliation: Department of Pathology, University of Vermont College of Medicine, Burlington 05405-0068, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Beddow
authors.forename: S A
authors.initials: SA
authors.lastname: Richards
authors.forename: N R
authors.initials: NR
authors.lastname: Orem
authors.forename: I G
authors.initials: IG
authors.lastname: Macara
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D018076:DNA, Complementary; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D015723:Gene Library; D006160:Guanosine Triphosphate / Q000378:metabolism; D006624:Hippocampus; D006801:Humans; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D011485:Protein Binding; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D020931:ran GTP-Binding Protein
chemical_list: D018076:DNA, Complementary; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; C091775:ran-binding protein 1; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein