title: Exportin 5 is a RanGTP-dependent dsRNA-binding protein that mediates nuclear export of pre-miRNAs.
abstract: microRNAs (miRNAs) are widespread among eukaryotes, and studies in several systems have revealed that miRNAs can regulate expression of specific genes. Primary miRNA transcripts are initially processed to approximately 70-nucleotide (nt) stem-loop structures (pre-miRNAs), exported to the cytoplasm, further processed to yield approximately 22-nt dsRNAs, and finally incorporated into ribonucleoprotein particles, which are thought to be the active species. Here we study nuclear export of pre-miRNAs and show that the process is saturable and thus carrier-mediated. Export is sensitive to depletion of nuclear RanGTP and, according to this criterion, mediated by a RanGTP-dependent exportin. An unbiased affinity chromatography approach with immobilized pre-miRNAs identified exportin 5 as the pre-miRNA-specific export carrier. We have cloned exportin 5 from Xenopus and demonstrate that antibodies raised against the Xenopus receptor specifically block pre-miRNA export from nuclei of Xenopus oocytes. We further show that exportin 5 interacts with double-stranded RNA in a sequence-independent manner.
authors.affiliation: Zentrum für Molekulare Biologie, Heidelberg, Germany.
authors.forename: Markus T
authors.initials: MT
authors.lastname: Bohnsack
authors.forename: Kevin
authors.initials: K
authors.lastname: Czaplinski
authors.forename: Dirk
authors.initials: D
authors.lastname: Gorlich
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D004330:Drosophila / Q000235:genetics; D006801:Humans; D028884:Karyopherins / Q000378:metabolism*; D035683:MicroRNAs / Q000096:biosynthesis*; D008969:Molecular Sequence Data; D011485:Protein Binding; D012322:RNA Precursors / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000378:metabolism; D012343:RNA, Transfer / Q000378:metabolism; D014981:Xenopus; D020931:ran GTP-Binding Protein
chemical_list: D028884:Karyopherins; D035683:MicroRNAs; D012322:RNA Precursors; D012330:RNA, Double-Stranded; C446511:XPO5 protein, human; D012343:RNA, Transfer; D020931:ran GTP-Binding Protein