Showing papers on "Importin published in 1992"
TL;DR: It is shown here that several of the abundant hnRNP proteins, including Al, shuttle between the nucleus and the cytoplasm, and may thus also have cy toplasmic functions.
Abstract: 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.
830 citations
TL;DR: U1A represents a novel class of protein which shuttles between cytoplasm and nucleus and whose intracellular distribution can be altered by the number of free binding sites for the protein present in the cytopLasm or the nucleus.
Abstract: Nuclear transport of the U1 snRNP-specific protein U1A has been examined. U1A moves to the nucleus by an active process which is independent of interaction with U1 snRNA. Nuclear localization requires an unusually large sequence element situated between amino acids 94 and 204 of the protein. U1A transport is not unidirectional. The protein shuttles between nucleus and cytoplasm. At equilibrium, the concentration of the protein in the nucleus and cytoplasm is not, however, determined solely by transport rates, but can be perturbed by introducing RNA sequences that can specifically bind U1A in either the nuclear or cytoplasmic compartment. Thus, U1A represents a novel class of protein which shuttles between cytoplasm and nucleus and whose intracellular distribution can be altered by the number of free binding sites for the protein present in the cytoplasm or the nucleus.
119 citations
TL;DR: Results indicate that even when the kinetics of transport are affected by amino acid substitutions, the long peptide directs the transport of large molecules such as IgM into the nucleus.
65 citations
TL;DR: A nuclear localization signal (NLS) has been identified in the N-terminal amino acid sequence of the polyomavirus major capsid protein VP1, and lysine-3 was crucial for nuclear transport, since substitution of this amino acid with threonine prevented nuclear localization of the microinjected, FITC-labeled conjugate.
48 citations
TL;DR: The genetic subtractive and biochemical additive approaches have identified the C-terminal sequence of polyoma-virus VP2 (containing amino acids Glu307-Leu318) as the NLS of this protein.
39 citations