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PMID:11046143

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Citation

Solsbacher, J, Maurer, P, Vogel, F and Schlenstedt, G (2000) Nup2p, a yeast nucleoporin, functions in bidirectional transport of importin alpha. Mol. Cell. Biol. 20:8468-79

Abstract

Import of proteins containing a classical nuclear localization signal (NLS) into the nucleus is mediated by importin alpha and importin beta. Srp1p, the Saccharomyces cerevisiae homologue of importin alpha, returns from the nucleus in a complex with its export factor Cse1p and with Gsp1p (yeast Ran) in its GTP-bound state. We studied the role of the nucleoporin Nup2p in the transport cycle of Srp1p. Cells lacking NUP2 show a specific defect in both NLS import and Srp1p export, indicating that Nup2p is required for efficient bidirectional transport of Srp1p across the nuclear pore complex (NPC). Nup2p is located at the nuclear side of the central gated channel of the NPC and provides a binding site for Srp1p via its amino-terminal domain. We show that Nup2p effectively releases the NLS protein from importin alpha-importin and beta and strongly binds to the importin heterodimer via Srp1p. Kap95p (importin beta) is released from this complex by a direct interaction with Gsp1p-GTP. These data suggest that besides Gsp1p, which disassembles the NLS-importin alpha-importin beta complex upon binding to Kap95p in the nucleus, Nup2p can also dissociate the import complex by binding to Srp1p. We also show data indicating that Nup1p, a relative of Nup2p, plays a similar role in termination of NLS import. Cse1p and Gsp1p-GTP release Srp1p from Nup2p, which suggests that the Srp1p export complex can be formed directly at the NPC. The changed distribution of Cse1p at the NPC in nup2 mutants also supports a role for Nup2p in Srp1p export from the nucleus.

Links

PubMed PMC102153

Keywords

Active Transport, Cell Nucleus; Binding Sites; Cell Nucleus/metabolism; Guanosine Triphosphate/metabolism; Karyopherins; Membrane Proteins/genetics; Membrane Proteins/metabolism; Monomeric GTP-Binding Proteins/metabolism; Mutation; Nuclear Localization Signals; Nuclear Pore Complex Proteins; Nuclear Proteins/genetics; Nuclear Proteins/metabolism; Porins/genetics; Porins/metabolism; Recombinant Proteins/genetics; Recombinant Proteins/metabolism; Saccharomyces cerevisiae Proteins; Yeasts/genetics; Yeasts/metabolism; alpha Karyopherins; beta Karyopherins

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

YEAST:NUP1

involved_in

GO:0006607: NLS-bearing protein import into nucleus

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete

YEAST:NUP1

part_of

GO:0005643: nuclear pore

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

YEAST:NUP2

involved_in

GO:0006611: protein export from nucleus

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete

YEAST:NUP2

involved_in

GO:0006607: NLS-bearing protein import into nucleus

ECO:0000314: direct assay evidence used in manual assertion

P

Seeded From UniProt

complete

YEAST:NUP2

involved_in

GO:0006607: NLS-bearing protein import into nucleus

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete

YEAST:NUP2

enables

GO:0017056: structural constituent of nuclear pore

ECO:0000353: physical interaction evidence used in manual assertion

SGD:S000005133

F

Seeded From UniProt

complete


See also

References

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