IDENTIFICATION OF A NUCLEAR EXPORT RECEPTOR FOR TRANSFER-RNA

Background: Transport of macromolecules between the nucleus and cytopl asm of eukaryotic cells is mediated by nuclear import and export recep tors. The receptors identified to date are members of a family of Ran GTPase-binding proteins whose founding member is importin-beta. Intera ction between these receptors and their cargo is regulated by the GTP- bound form of Ran. Export complexes form and import complexes disassem ble on binding of RanGTP to the receptor. Yeast Los1p is a member of t he importin-beta family with a poorly defined role in tRNA production. Results: A human member of the importin-beta family that is distantly related to Los1p (21% identity) has been characterized. The protein s huttled 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 tR NA from the nucleus and in relief of the competitive inhibition of tRN A export caused by the introduction of saturating amounts of nuclear t RNA. Conclusions: The human protein has the functional properties expe cted of a transport receptor that mediates export of tRNA from the nuc leus. We therefore name the protein Exportin(tRNA). (C) Current Biolog y Ltd ISSN 0960-9822.