Shuttling of pre-mRNA binding proteins between nucleus and cytoplasm.
RNA polymerase II transcripts, heterogeneous nuclear RNAs (hnRNAs), associate in the nucleus with specific proteins that bind premessenger RNA (hnRNP proteins) and with small nuclear ribonucleoprotein particles (snRNPs). These hnRNA-hnRNP-snRNP complexes assemble on nascent transcripts and hnRNA is processed to mRNA in them. HnRNP proteins have been localized to the nucleoplasm and their functions were presumed to be limited to nuclear events in mRNA biogenesis. It was proposed that an exchange of hnRNP for mRNA-binding proteins accompanies transport of mRNA from the nucleus to the cytoplasm. We show here that several of the abundant hnRNP proteins, including A1, shuttle between the nucleus and the cytoplasm. HnRNP proteins may thus also have cytoplasmic functions. Furthermore, when in the cytoplasm, A1 is bound to mRNA and RNA polymerase II transcription is necessary before it can return to the nucleus. We propose that the cytoplasmic ribonucleoprotein complex of mRNA with hnRNP proteins is the substrate of nuclear-cytoplasmic transport of mRNA.
Piñol-Roma
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S
Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia 19104-6148.
Dreyfuss
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G
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism*; D004257:DNA Polymerase II / Q000037:antagonists & inhibitors; D003609:Dactinomycin / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006801:Humans; D011061:Poly A / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D014466:Ultraviolet Rays; D014982:Xenopus laevis
D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012333:RNA, Messenger; D012261:Ribonucleoproteins; D003609:Dactinomycin; D011061:Poly A; D012313:RNA; D004257:DNA Polymerase II