Protein import into the nucleus

Schlenstedt, Gabriel

doi:10.1016/0014-5793(96)00583-2

Cited by 51 publications

(40 citation statements)

References 83 publications

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“…RanBP1 contains a RanGTP-binding domain different from that of importin ␤. Yrb1p, the yeast homologue of RanBP1, is an essential cytoplasmic protein which is required for nucleocytoplasmic transport (reviewed in reference 61).…”

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Cse1p Is Involved in Export of Yeast Importin α from the Nucleus

Solsbacher

Maurer

Bischoff

et al. 1998

Molecular and Cellular Biology

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Proteins bearing a nuclear localization signal (NLS) are targeted to the nucleus by the heterodimeric transporter importin. Importin ␣ binds to the NLS and to importin ␤, which carries it through the nuclear pore complex (NPC). Importin disassembles in the nucleus, evidently by binding of RanGTP to importin ␤. The importin subunits are exported separately. We investigated the role of Cse1p, the Saccharomyces cerevisiae homologue of human CAS, in nuclear export of Srp1p (yeast importin ␣). Cse1p is located predominantly in the nucleus but also is present in the cytoplasm and at the NPC. We analyzed the in vivo localization of the importin subunits fused to the green fluorescent protein in wild-type and cse1-1 mutant cells. Srp1p but not importin ␤ accumulated in nuclei of cse1-1 mutants, which are defective in NLS import but not defective in NLS-independent import pathways. Purified Cse1p binds with high affinity to Srp1p only in the presence of RanGTP. The complex is dissociated by the cytoplasmic RanGTP-binding protein Yrb1p. Combined with the in vivo results, this suggests that a complex containing Srp1p, Cse1p, and RanGTP is exported from the nucleus and is subsequently disassembled in the cytoplasm by Yrb1p. The formation of the trimeric Srp1p-Cse1p-RanGTP complex is inhibited by NLS peptides, indicating that only NLS-free Srp1p will be exported to the cytoplasm.Transport of proteins and RNAs between the cytoplasm and the nucleus across the nuclear pore complex (NPC) is mediated by shuttling transport receptors. All transporters so far identified belong to the importin ␤ superfamily. Substrate binding and release of these transporters are modulated by the small GTPase Ran, the key regulator of nucleocytoplasmic transport. Several specific transport pathways for different import and export substrates have recently been identified (reviewed in references 52 and 73).The best understood transport pathway is the import of proteins carrying a classical nuclear localization sequence (NLS), which is characterized by a short segment of basic amino acid residues (20). The NLS is recognized by importin ␣ in the cytoplasm, which in turn binds to importin ␤. Importin ␤ mediates docking at the NPC and subsequent transport into the nucleus. Docking of NLS substrates to the nuclear envelope and subsequent energy-dependent transfer into the nucleus can be reconstituted with recombinant factors and permeabilized cells in vitro. Two soluble factors, Ran and p10, are sufficient to promote the translocation step (for reviews, see references 16, 32 and 50).Ran is an abundant, mostly nuclear protein that switches between two conformational states, i.e., bound to GDP (RanGDP) and to GTP (RanGTP). The specific regulators of the Ran GTPase cycle, the cytoplasmic GTPase-activating protein RanGAP1/Rna1p and the nuclear nucleotide exchange factor RCC1/Prp20p, generate RanGDP in the cytoplasm and RanGTP in the nucleus (reviewed in references 32 and 61). RanGTP binds to importin ␤, which is thereby released from the NLS-importin complex (...

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confidence: 99%

Cse1p Is Involved in Export of Yeast Importin α from the Nucleus

Solsbacher

Maurer

Bischoff

et al. 1998

Molecular and Cellular Biology

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119

127

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“…The Ran protein (Ras-related nuclear protein) is a member of the Ras superfamily of small nuclear GTPase, which is believed to be involved in normal cell cycle progression and in the transport of RNA and proteins between the nucleus and cytoplasm [2,[13][14][15][16]. Proteins interact with Ran at the GDP-or GTP-bound state, thereby regulating their transport through NPCs [27].…”

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Molecular Cloning and Characterization of a Novel Testis-Specific Nucleoporin-Related Gene

Hd²,

Sy³

et al. 1999

Archives of Andrology

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“…Immunoelectron microscopy has demonstrated that RanBP2/Nup358 localizes to the cytoplasmic fibrils [21,22,[35][36][37], whereas Nupl53 and Nup98 are constit uents of the nuclear basket [18,22,38,39]. These find ings have provided the basis for several transport mod els in which FG-repeat-containing nucleoporins form a static array of docking sites that transiently interact with transport complexes [8,9,15].…”

Section: Discussionmentioning

confidence: 99%

“…Protein import into the nucleus is mediated by a heterodimer comprising the nuclear localization sig nal (NLS)-receptor/importin a, which recognizes the NLSs of karyophilic proteins, and nuclear import fac tor p97/importin /?, which contacts the NPC [re viewed by 6; see also [7][8][9], After this first docking step, the ligand complex is imported via an energydependent process th a t requires the small GTPase Ran/TC4 [10,11]. GTP hydrolysis by Ran is though to drive the translocation reaction [12][13][14], which may involve repeated association and dissociation of im port complex components to the NPC [15,16], or the movement of a single complex across the NPC either in discrete steps [17] or in a sliding motion [9].…”

Section: Introductionmentioning

confidence: 99%

“…GTP hydrolysis by Ran is though to drive the translocation reaction [12][13][14], which may involve repeated association and dissociation of im port complex components to the NPC [15,16], or the movement of a single complex across the NPC either in discrete steps [17] or in a sliding motion [9]. Many FG-repeat-containing nucleoporins are located at distinct positions along the NPC and may form bind ing sites for transport complexes [15,18,19].…”

Section: Introductionmentioning

confidence: 99%

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The Nucleoporin CAN/Nup214 Binds to both the Cytoplasmic and the Nucleoplasmic Sides of the Nuclear Pore Complex in Overexpressing Cells

Boer

Deursen

Croes

et al. 1997

Experimental Cell Research

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CAN/Nup214, an essential com ponent of th e v e rte b ra te n u clear pore complex (NPC), is re q u ire d for p ro p er cell cycle progression an d nucleocytoplasm ic tra n sp o rt. It is a m em ber of th e FG -repeat-containing fam ily of nucleoporins an d has b een localized to th e cytoplasm ic face of th e NPC. In d ire c t im m unofluores cence studies w ith specific antibodies have show n th a t m oderate overexpression of h u m an CAN in HeLa cells causes an increase in CAN/Nup214 levels a t th e n u clear envelope. Here, we dem o n strate th a t in such HeLa cells, CAN/Nup214 does n o t localize exclusively to th e cytoplasm ic side of th e NPC. Cryosections, stain ed w ith CAN-specific antibodies an d exam ined by elec tro n m icroscopy, show ed th a t ab o u t one-third of th e gold-labeled NPCs w ere d eco rated a t th e cytoplasm ic face and th e rem aining tw o-thirds a t th e nucleoplas mic face. These d ata in d icate th a t b o th th e cytoplasm ic fibrils an d th e n u clear b ask et of th e v e rte b ra te NPC contain specific binding sites for e ith e r CAN/Nup214 or for its in terac tin g p ro tein s, Nup88 and hCRM l. Thus, it is conceivable th a t CAN/Nup214 functions in nucleocytoplasm ic tra n sp o rt a t b o th faces of th e NPC.

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Protein import into the nucleus

Cited by 51 publications

References 83 publications

Cse1p Is Involved in Export of Yeast Importin α from the Nucleus

Cse1p Is Involved in Export of Yeast Importin α from the Nucleus

Molecular Cloning and Characterization of a Novel Testis-Specific Nucleoporin-Related Gene

The Nucleoporin CAN/Nup214 Binds to both the Cytoplasmic and the Nucleoplasmic Sides of the Nuclear Pore Complex in Overexpressing Cells

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