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      A Small Ubiquitin-Related Polypeptide Involved in Targeting RanGAP1 to Nuclear Pore Complex Protein RanBP2

      , , , ,
      Cell
      Elsevier BV

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          Abstract

          We have found that the mammalian Ran GTPase-activating protein RanGAP1 is highly concentrated at the cytoplasmic periphery of the nuclear pore complex (NPC), where it associates with the 358-kDa Ran-GTP-binding protein RanBP2. This interaction requires the ATP-dependent posttranslational conjugation of RanGAP1 with SUMO-1 (for small ubiquitin-related modifier), a novel protein of 101 amino acids that contains low but significant homology to ubiquitin. SUMO-1 appears to represent the prototype for a novel family of ubiquitin-related protein modifiers. Inhibition of nuclear protein import resulting from antibodies directed at NPC-associated RanGAP1 cannot be overcome by soluble cytosolic RanGAP1, indicating that GTP hydrolysis by Ran at RanBP2 is required for nuclear protein import.

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          Most cited references38

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          The GTPase superfamily: a conserved switch for diverse cell functions.

          Proteins that bind and hydrolyse GTP are being discovered at a rapidly increasing rate. Each of these many GTPases acts as a molecular switch whose 'on' and 'off' states are triggered by binding and hydrolysis of GTP. Conserved structure and mechanism in myriad versions of the switch--in bacteria, yeast, flies and vertebrates--suggest that all derive from a single primordial protein, repeatedly modified in the course of evolution to perform a dazzling variety of functions.
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            Nucleocytoplasmic transport.

            Active transport of proteins and RNAs between the nucleus and cytoplasm is a major process in eukaryotic cells. Recently, factors that recognize transport substrates and mediate nuclear import or export have been characterized, revealing interactions that target substrates to the nuclear pore complexes, through which translocation occurs. Translocation requires energy, and for the import process this energy is at least partly consumed by the action of the small guanosine triphosphatase Ran. In the first half of the review, some of the well-established general background information on nucleocytoplasmic transport is discussed. The second half describes recent information on the mechanistic details of nuclear import and export as well as major unresolved issues such as how directionality is conferred on either import or export. The whole review is slanted toward discussion of metazoan cells.
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              Protein import into nuclei: association and dissociation reactions involving transport substrate, transport factors, and nucleoporins.

              The molecular dynamics of nuclear protein import were examined in a solution binding assay by testing for interactions between a protein containing a nuclear localization signal (NLS), the transport factors karyopherin alpha, karyopherin beta, and Ran, and FXFG or GLFG repeat regions of nucleoporins. We found that karyopherins alpha and beta cooperate to bind FXFG but not GLFG repeat regions. Binding of the NLS protein to karyopherin alpha was enhanced by karyopherin beta. Two novel reactions were discovered. First, incubation of a karyopherin heterodimer-NLS protein complex with an FXFG repeat region stimulated the dissociation of the NLS protein from the karyopherin heterodimer. Second, incubation of the karyopherin heterodimer with RanGTP (or with a Ran mutant that cannot hydrolyze GTP) led to the dissociation of karyopherin alpha from beta and to an association of Ran with karyopherin beta; RanGDP had no effect. We propose that movement of NLS proteins across the nuclear pore complex is a stochastic process that operates via repeated association-dissociation reactions.
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                Author and article information

                Journal
                Cell
                Cell
                Elsevier BV
                00928674
                January 1997
                January 1997
                : 88
                : 1
                : 97-107
                Article
                10.1016/S0092-8674(00)81862-0
                9019411
                58166bee-0f32-47f6-95bc-714bc703f0b6
                © 1997

                https://www.elsevier.com/tdm/userlicense/1.0/

                https://www.elsevier.com/open-access/userlicense/1.0/

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