Most nuclear proteins are imported by a single pathway.
Using kinetic competition analysis, we show that the import of most Xenopus oocyte nuclear proteins is directed by a single family of nuclear localization signals (NLS). The transport of microinjected [35S]methionine-labeled nuclear proteins into oocyte nuclei was challenged with saturating concentrations of SV40 large T-antigen NLS peptide-BSA (P(Lys)-BSA) and was assessed by SDS-acrylamide gel electrophoresis and fluorography. P(Lys)-BSA was effective at competing the import of virtually all larger polypeptides but had a less marked effect on the mediated import of many smaller polypeptides. Wheat germ agglutinin, an inhibitor of nuclear pore complex function, enhanced the competitive effects of P(Lys)-BSA on the import of both large and small polypeptides. These data indicate that most 35S-labeled Xenopus oocyte nuclear proteins, including nucleoplasmin, contain NLSs that are functionally related to the T-antigen NLS and probably employ the same cytosolic NLS receptor(s).
Michaud
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Department of Biology, University of Rochester, New York 14627.
Goldfarb
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DS
D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D002451:Cell Compartmentation; D002467:Cell Nucleus / Q000378:metabolism*; D004527:Egg Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D056489:Nucleoplasmins; D010750:Phosphoproteins; D011107:Polylysine / Q000378:metabolism; D012315:RNA Caps / Q000378:metabolism; D013329:Structure-Activity Relationship; D014909:Wheat Germ Agglutinins / Q000494:pharmacology; D014982:Xenopus laevis
D004527:Egg Proteins; D009687:Nuclear Proteins; D056489:Nucleoplasmins; D010750:Phosphoproteins; D012315:RNA Caps; D014909:Wheat Germ Agglutinins; D011107:Polylysine