Assembly and nuclear transport of the U4 and U4/U6 snRNPs.
We have analyzed the assembly of the spliceosomal U4/U6 snRNP by injecting synthetic wild-type and mutant U4 RNAs into the cytoplasm of Xenopus oocytes and determining the cytoplasmic-nuclear distribution of U4 and U4/U6 snRNPs by CsCl density gradient centrifugation. Whereas the U4 snRNP was localized in both the cytoplasmic and nuclear fractions, the U4/U6 snRNP was detected exclusively in the nuclear fraction. Cytoplasmic-nuclear migration of the U4 snRNP did not depend on the stem II nor on the 5' stem-loop region of U4 RNA. Our data provide strong evidence that, following the cytoplasmic assembly of the U4 snRNP, the interaction of the U4 snRNP with U6 RNA/RNP occurs in the nucleus; furthermore, cytoplasmic-nuclear transport of the U4 snRNP is independent of U4/U6 snRNP assembly.
Max-Planck-Institut für Molekulare Genetik, Otto-Warburg-Laboratorium, Berlin Dahlem, Germany.
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Wersig
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Guddat
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Pieler
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Bindereif
D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D008845:Microinjections; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D012313:RNA / Q000235:genetics; D012261:Ribonucleoproteins / Q000235:genetics* / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear; D014158:Transcription, Genetic; D014982:Xenopus laevis
D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear; D012313:RNA