title: Arabidopsis transportin1 is the nuclear import receptor for the circadian clock-regulated RNA-binding protein AtGRP7.
abstract: We characterized the Arabidopsis orthologue of the human nuclear import receptor transportin1 (TRN1). Like the human receptor, Arabidopsis TRN1 recognizes nuclear import signals on proteins that are different from the classical basic nuclear localization signals. The M9 domain of human heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) is the prototype of such signals. We show that AtTRN1 binds to similar domains in hnRNP-like proteins from plants. AtTRN1 also interacts with human hnRNP A1 and with yeast Nab2p, two classical import cargo proteins of transportin in these organisms. Like all nuclear transport receptors of the importin-beta family, AtTRN1 binds to the regulatory GTPase Ran from Arabidopsis. We demonstrated that the amino terminus of AtTRN1 is necessary for this interaction. Recombinant AtTRN1 conferred nuclear import of fluorescently labelled BSA-M9 peptide conjugates in permeabilized HeLa cells, functionally replacing human TRN1 in these in vitro nuclear import assays. We identified three plant substrate proteins that interact with AtTRN1 and contain M9-like domains: a novel Arabidopsis hnRNP that shows high similarity to human hnRNP A1 and two small RNA-binding proteins from Arabidopsis, AtGRP7 and AtGRP8. Nuclear import activity of the M9-like domains of these plant proteins was demonstrated in vivo by their ability to confer partial nuclear re-localisation of a GFP fusion protein containing a nuclear export signal. In addition, fluorescently labelled AtGRP7 was specifically imported into nuclei of permeabilized HeLa cells by Arabidopsis AtTRN1 and human TRN1. These results suggest that the transportin-mediated nuclear import pathway is highly conserved between man, yeast and plants.
authors.affiliation: Institute of Biology II, Cell Biology, University of Freiburg, Schänzlestrassse 1, 79104 Freiburg, Germany.
authors.forename: Alicja
authors.initials: A
authors.lastname: Ziemienowicz
authors.forename: Dorothea
authors.initials: D
authors.lastname: Haasen
authors.forename: Dorothee
authors.initials: D
authors.lastname: Staiger
authors.forename: Thomas
authors.initials: T
authors.lastname: Merkle
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000235:genetics* / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D011485:Protein Binding; D021381:Protein Transport; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D049452:Green Fluorescent Proteins; D028884:Karyopherins; D008164:Luminescent Proteins; D016601:RNA-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; C118496:GRP7 protein, Arabidopsis; C482062:TRN1 protein, Arabidopsis