title: High levels of the GTPase Ran/TC4 relieve the requirement for nuclear protein transport factor 2.
abstract: The GTPase Ran/TC4 and the 14-kDa protein nuclear transport factor 2 (NTF2) are two of the cytosolic factors that mediate nuclear protein import in vertebrates. Previous biochemical studies have shown that NTF2 binds directly to the GDP-bound form of Ran/TC4 and to proteins of the nuclear pore complex that contain phenylalanine-glycine repeats. In the present study we have used molecular genetic approaches to study the Saccharomyces cerevisiae homologue of NTF2. The scNTF2 gene encodes a protein that is 44% identical to the human protein. We found that deletion of the scNTF2 gene is lethal and that repression of NTF2p expression by a regulatable promoter results in gross structural distortions of the nuclear envelope. In a screen for high copy number suppressors of a scNTF2 deletion, the only gene we isolated other than scNTF2 itself was GSP1, the S. cerevisiae homologue of Ran/TC4. Furthermore, we found that high levels of Ran/TC4 can relieve the requirement for NTF2 in a mammalian-permeabilized cell assay for nuclear protein import. These data suggest that certain of the nuclear protein import functions of NTF2 and Ran/TC4 are closely linked and that NTF2 may serve to modulate a transport step involving Ran/TC4.
authors.affiliation: Departments of Cell and Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA. paschal@virginia.edu
authors.forename: B M
authors.initials: BM
authors.lastname: Paschal
authors.forename: C
authors.initials: C
authors.lastname: Fritze
authors.forename: T
authors.initials: T
authors.lastname: Guan
authors.forename: L
authors.initials: L
authors.lastname: Gerace
mesh_terms: D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D017353:Gene Deletion; D005800:Genes, Fungal; D016153:Genes, Suppressor; D005816:Genetic Complementation Test; D006579:Heterozygote; D020559:Monomeric GTP-Binding Proteins; D009687:Nuclear Proteins / Q000378:metabolism*; D029543:Nucleocytoplasmic Transport Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D020931:ran GTP-Binding Protein
chemical_list: D002352:Carrier Proteins; C080324:GSP1 protein, S cerevisiae; D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins; D029701:Saccharomyces cerevisiae Proteins; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020559:Monomeric GTP-Binding Proteins; D020931:ran GTP-Binding Protein