Identification of a nuclear export receptor for tRNA

Abstract

Background: Transport of macromolecules between the nucleus and cytoplasm of eukaryotic cells is mediated by nuclear import and export receptors. The receptors identified to date are members of a family of Ran GTPase-binding proteins whose founding member is importin-β. Interaction between these receptors and their cargo is regulated by the GTP-bound form of Ran. Export complexes form and import complexes disassemble on binding of RanGTP to the receptor. Yeast Los1p is a member of the importin-β family with a poorly defined role in tRNA production.Results: A human member of the importin-β family that is distantly related to Los1p (21% identity) has been characterized. The protein shuttled between the nucleus and cytoplasm and interacts with tRNA in a RanGTP-dependent manner. Injection of the protein into the nuclei of Xenopus oocytes resulted in a specific stimulation of the export of tRNA from the nucleus and in relief of the competitive inhibition of tRNA export caused by the introduction of saturating amounts of nuclear tRNA.Conclusions: The human protein has the functional properties expected of a transport receptor that mediates export of tRNA from the nucleus. We therefore name the protein Exportin(tRNA).