title: Microinjected U snRNAs are imported to oocyte nuclei via the nuclear pore complex by three distinguishable targeting pathways.
abstract: The inhibitory effects of wheat germ agglutinin and mAb 414 on the nuclear import of all types of U snRNAs indicate that they cross the nuclear envelope through the nuclear pore complex. However, the import of different U snRNAs occurs by kinetically distinct targeting pathways that can be distinguished from one another by the competitive effects of free trimethylguanosine cap dinucleotide (m3GpppG) and P(Lys)-BSA, an efficient synthetic karyophile based on the nuclear localization signal of SV40 large T antigen. The import of U snRNAs that contain 5' m3GpppN caps and are complexed by Sm proteins (U1, U2, U4, and U5) is competed by coinjection with free m3GpppG, indicating a shared transport factor, but not by P(Lys)-BSA. The import of U6 snRNA, which lacks a m3GpppN cap and is not complexed by the Sm proteins, is competed by P(Lys)-BSA but not by free m3GpppG. Thus, by the criterion of kinetic competition, U6 snRNA import is identical to that of the karyophilic proteins P(Lys)-BSA and nucleoplasmin. Uniquely, the import of U3 snRNA, which contains a m3GpppN cap but does not bind Sm proteins is not competed by either free m3GpppG or P(Lys)-BSA. Thus, U3 snRNA appears to be imported by a novel third kinetic pathway.
authors.affiliation: Department of Biology, University of Rochester, New York 14627.
authors.forename: N
authors.initials: N
authors.lastname: Michaud
authors.forename: D
authors.initials: D
authors.lastname: Goldfarb
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008845:Microinjections; D008969:Molecular Sequence Data; D009685:Nuclear Envelope / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D012314:RNA Cap Analogs / Q000494:pharmacology; D012342:RNA, Small Nuclear / Q000378:metabolism*; D012261:Ribonucleoproteins / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear; D014909:Wheat Germ Agglutinins; D014981:Xenopus
chemical_list: D012314:RNA Cap Analogs; D012342:RNA, Small Nuclear; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D014909:Wheat Germ Agglutinins