title: Mutations within the Ran/TC4 GTPase. Effects on regulatory factor interactions and subcellular localization.
abstract: Ran, a member of the Ras superfamily of GTPases, is predominantly localized in the nucleus and is a necessary component in the active transport of proteins through nuclear pores. Disruption of Ran function affects the regulation of mitosis, DNA synthesis, and RNA processing and export. To explore the mechanisms of Ran function, mutants of the Ran GTPase were characterized, several of which are capable of dominantly interfering with nuclear protein import. Unlike wild-type Ran, the putative gain-of-function mutant (G19V Ran) was not sensitive to the exchange factor, RCC1. In addition the G19V Ran and effector domain mutants (L43E and E46G Ran) were not sensitive to the GTPase-activating protein, Fug1. Epitope-tagged G19V Ran and L43E Ran isolated from transfected BHK21 cells were each about 50% GTP-bound, whereas the wild-type and a C-terminal deletion mutant (Delta-DE Ran) were primarily bound to GDP. While G19V Ran interacted with known Ran-binding proteins and with an isolated Ran-binding domain, the T24N Ran did not, and binding by L43E Ran was substantially reduced. Wild-type HA1-tagged Ran expressed in BHK21 cells was nuclear, whereas the G19V, T24N, L43E, and E46G forms of Ran were predominantly localized at the nuclear envelope, and Delta-DE Ran was primarily cytosolic. Similar results were observed when permeabilized BHK21 cells were incubated with extracts of COS cells expressing the mutants. Thus mutations that affect the interaction of Ran with regulatory proteins and effectors can disrupt the normal subcellular localization of Ran, lending support for the current model of Ran-mediated nuclear import.
authors.affiliation: Department of Pathology and Comprehensive Cancer Center, University of Vermont, Burlington, Vermont 05405, USA. klounsbu@200.uvm.edu
authors.forename: K M
authors.initials: KM
authors.lastname: Lounsbury
authors.forename: S A
authors.initials: SA
authors.lastname: Richards
authors.forename: K L
authors.initials: KL
authors.lastname: Carey
authors.forename: I G
authors.initials: IG
authors.lastname: Macara
mesh_terms: D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism*; D002451:Cell Compartmentation; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000378:metabolism; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D015398:Signal Transduction; D013329:Structure-Activity Relationship; D020931:ran GTP-Binding Protein
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D009687:Nuclear Proteins; C092317:RANGAP1 protein, human; C062521:RCC1 protein, human; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D020931:ran GTP-Binding Protein