Nuclear tRNA aminoacylation and its role in nuclear export of endogenous tRNAs in Saccharomyces cerevisiae

Nuclear tRNA aminoacylation was proposed to provide a proofreading step in Xenopus oocytes, ensuring nuclear export of functional tRNAs [Lund. E. & Da hlberg, J. E. (1998) Science 282, 2082-2085]. Herein, it is documented that tRNA aminoacylation also occurs in yeast nuclei and is important for tRNA export. We propose that tRNA aminoacylation functions in one of at least tw o parallel paths of tRNA export in yeast. Alteration of one aminoacyl-tRNA synthetase affects export of only cognate tRNA, whereas alterations of two other aminoacyl-tRNA synthetases affect export of both cognate and noncogna te tRNAs. Saturation of tRNA export pathway is a possible explanation of th is phenomenon.