Multiple pathways in nuclear transport: the import of U2 snRNP occurs by a novel kinetic pathway.
Protein import to the nucleus is a signal-mediated process that exhibits saturation kinetics. We investigated whether signal bearing proteins compete with U2 and U6 snRNPs during import. When injected into Xenopus oocytes, saturating concentrations of P(Lys)-BSA, a protein bearing multiple nuclear localization signals from SV40 large T-antigen, reduce the rate of [125I]P(Lys)-BSA and of [125I]nucleoplasmin import, consistent with their competing for and sharing the same limiting component of the import apparatus. In contrast, saturating concentrations of P(Lys)-BSA do not reduce the rate of HeLa [32P]U2 snRNP assembly or import. The import of U6 snRNP is also competed by P(Lys)-BSA. We conclude that U2 snRNP is imported into oocyte nuclei by a kinetic pathway that is distinct from the one followed by P(Lys)-BSA, nucleoplasmin, and U6 snRNP.
Michaud
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Department of Biology, University of Rochester, New York 14627.
Goldfarb
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D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D009865:Oocytes / Q000378:metabolism; D011233:Precipitin Tests; D012261:Ribonucleoproteins / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear; D012710:Serum Albumin, Bovine / Q000378:metabolism; D015398:Signal Transduction; D014982:Xenopus laevis
D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D012710:Serum Albumin, Bovine