title: XMog1, a nuclear ran-binding protein in Xenopus, is a functional homologue of Schizosaccharomyces pombe mog1p that co-operates with RanBP1 to control generation of Ran-GTP.
abstract: Ran is a multifunctional small GTPase of the Ras superfamily that plays roles in nucleocytoplasmic transport, mitotic spindle assembly and nuclear envelope formation. By screening a Xenopus oocyte cDNA library for Ran-GTP-binding proteins using the two-hybrid system of co-expression in yeast, we identified XMog1, a 20.4 kDa polypeptide related to Mog1p in Saccharomyces cerevisiae and similar gene products in Schizosaccharomyces pombe, Arabidopsis and mammals. We show that cDNAs encoding XMog1 and S. cerevisiae Mog1p rescue the growth defect of S. pombe cells lacking mog1, demonstrating conservation of their functions. In Xenopus somatic cells and transfected mammalian cells, XMogl is localised to the nucleus. XMog1 alone does not stimulate Ran GTPase activity or nucleotide exchange, but causes nucleotide release from Ran-GTP and forms a complex with nucleotide-free Ran. However, in combination with Ran-binding protein 1 (RanBP1), XMog1 promotes the release of GDP and the selective binding of GTP to Ran. XMog1 and RanBP1 also promote selective GTP loading onto Ran catalysed by the nuclear guanine nucleotide exchange factor, RCC1. We propose that Mog1-related proteins, together with RanBP1, facilitate the generation of Ran-GTP from Ran-GDP in the nucleus.
authors.affiliation: Biomedical Research Centre, University of Dundee, Ninewells Hospital and Medical School, Dundee, UK.
authors.forename: F J
authors.initials: FJ
authors.lastname: Nicolás
authors.forename: W J
authors.initials: WJ
authors.lastname: Moore
authors.forename: C
authors.initials: C
authors.lastname: Zhang
authors.forename: P R
authors.initials: PR
authors.lastname: Clarke
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018797:Cell Cycle Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D017353:Gene Deletion; D020043:Genes, Essential / Q000235:genetics; D005800:Genes, Fungal / Q000235:genetics; D005816:Genetic Complementation Test; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000737:chemistry* / Q000235:genetics / Q000254:growth & development; D029702:Schizosaccharomyces pombe Proteins; D013379:Substrate Specificity; D020798:Two-Hybrid System Techniques; D014981:Xenopus / Q000235:genetics; D029867:Xenopus Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; C499304:RCC1 protein, Xenopus; C062521:RCC1 protein, human; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D029867:Xenopus Proteins; C091775:ran-binding protein 1; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; C498734:mog1 protein, S pombe; D020931:ran GTP-Binding Protein