The shuttling SR protein 9G8 plays a role in translation of unspliced mRNA containing a constitutive transport element.
The splicing regulatory SR protein, 9G8, has recently been proposed to function in mRNA export in conjunction with the export protein, Tap/NXF1. Tap interacts directly with the Mason-Pfizer monkey virus constitutive transport element (CTE), an element that enables export of unspliced, intron-containing mRNA. Based on our previous finding that Tap can promote polysome association and translation of CTE-RNA, we investigated the effect of 9G8 on cytoplasmic RNA fate. 9G8 was shown to enhance expression of unspliced RNA containing either the Mason-Pfizer monkey virus-CTE or the recently discovered Tap-CTE. 9G8 also enhanced polyribosome association of unspliced RNA containing a CTE. Hyperphosphorylated 9G8 was present in monosomes and small polyribosomes, whereas soluble fractions contained only hypophosphorylated protein. Our results are consistent with a model in which hypophosphorylated SR proteins remain stably associated with messenger ribonucleoprotein (mRNP) complexes during export and are released during translation initiation concomitant with increased phosphorylation. These results provide further evidence for crucial links between RNA splicing, export and translation.
Swartz
Jennifer E
JE
Myles H. Thaler Center for AIDS and Human Retrovirus Research and Department of Microbiology, University of Virginia, Charlottesville, Virginia 22908, USA.
Bor
Yeou-Cherng
YC
Misawa
Yukiko
Y
Rekosh
David
D
Hammarskjold
Marie-Louise
ML
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D005091:Exons / Q000502:physiology; D006801:Humans; D016093:Mason-Pfizer monkey virus / Q000378:metabolism*; D008954:Models, Biological; D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins / Q000378:metabolism*; D010442:Peptide Chain Initiation, Translational / Q000502:physiology*; D010766:Phosphorylation; D011132:Polyribosomes / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012326:RNA Splicing / Q000502:physiology*; D012367:RNA, Viral / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D000068103:Serine-Arginine Splicing Factors
D009687:Nuclear Proteins; D029543:Nucleocytoplasmic Transport Proteins; D012367:RNA, Viral; D016601:RNA-Binding Proteins; D000068103:Serine-Arginine Splicing Factors