A conserved Drosophila transportin-serine/arginine-rich (SR) protein permits nuclear import of Drosophila SR protein splicing factors and their antagonist repressor splicing factor 1.
Members of the highly conserved serine/arginine-rich (SR) protein family are nuclear factors involved in splicing of metazoan mRNA precursors. In mammals, two nuclear import receptors, transportin (TRN)-SR1 and TRN-SR2, are responsible for targeting SR proteins to the nucleus. Distinctive features in the nuclear localization signal between Drosophila and mammalian SR proteins prompted us to examine the mechanism by which Drosophila SR proteins and their antagonist repressor splicing factor 1 (RSF1) are imported into nucleus. Herein, we report the identification and characterization of a Drosophila importin beta-family protein (dTRN-SR), homologous to TRN-SR2, that specifically interacts with both SR proteins and RSF1. dTRN-SR has a broad localization in the cytoplasm and the nucleus, whereas an N-terminal deletion mutant colocalizes with SR proteins in nuclear speckles. Far Western experiments established that the RS domain of SR proteins and the GRS domain of RSF1 are required for the direct interaction with dTRN-SR, an interaction that can be modulated by phosphorylation. Using the yeast model system in which nuclear import of Drosophila SR proteins and RSF1 is impaired, we demonstrate that complementation with dTRN-SR is sufficient to target these proteins to the nucleus. Together, the results imply that the mechanism by which SR proteins are imported to the nucleus is conserved between Drosophila and humans.
Institut de Génétique Moléculaire, Unité Mixte Recherche 5535 du Centre National de la Recherche Scientifique, l'Institut Fédératif de Recherches 24, F34293 Montpellier, France.
Eric
E
Allemand
Svetlana
S
Dokudovskaya
Rémy
R
Bordonné
Jamal
J
Tazi
D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism; D011485:Protein Binding; D019154:Protein Splicing; D017434:Protein Structure, Tertiary; D000072260:RNA Splicing Factors; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015003:Yeasts / Q000235:genetics / Q000378:metabolism; D028961:beta Karyopherins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D029721:Drosophila Proteins; D009687:Nuclear Proteins; D000072260:RNA Splicing Factors; D016601:RNA-Binding Proteins; C120397:RSF1 protein, Drosophila; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D012097:Repressor Proteins; D028961:beta Karyopherins; C119888:transportin SR