title: A family of proteins that stabilize the Ran/TC4 GTPase in its GTP-bound conformation.
abstract: Ran/TC4, referred to here as Ran1, is a 25-kilodalton nuclear GTP-binding protein with an acidic C terminus that lacks any consensus prenylation sites. Here, we use a nitrocellulose overlay assay to identify potential effector proteins that bind specifically and with high affinity to the GTP-bound form of Ran1. GTP-Ran1 is shown to bind a variety of proteins, present in many eukaryotic tissues and cell extracts. A 28-kDa protein is cytosolic, whereas others, consisting of proteins of 86-300 kDa, are primarily localized in the nucleus. Binding is highly specific and is not detected by other small GTPases, such as c-Ha-Ras or Rab3A. Both deletion of the C-terminal-DEDDDL acidic sequence or alteration of the N terminus of Ran1 inhibits binding. However, these altered forms of Ran1 maintain the capacity to bind guanyl nucleotides and interact with the nucleotide exchange factor. The Ran1-binding proteins potently inhibit release of GTP from Ran1. These proteins can therefore maintain Ran1 in the "on" state and are potential down-stream effectors for Ran1-dependent cellular processes.
authors.affiliation: Department of Pathology, University of Vermont Medical College, Burlington 05405-0068.
authors.forename: K M
authors.initials: KM
authors.lastname: Lounsbury
authors.forename: A L
authors.initials: AL
authors.lastname: Beddow
authors.forename: I G
authors.initials: IG
authors.lastname: Macara
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism; D004355:Drug Stability; D004591:Electrophoresis, Polyacrylamide Gel; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D006160:Guanosine Triphosphate / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017368:Protein Prenylation; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D017384:Sequence Deletion; D020931:ran GTP-Binding Protein
chemical_list: D002352:Carrier Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D006160:Guanosine Triphosphate; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein