An aminoacylation-dependent nuclear tRNA export pathway in yeast

Yeast Los1p, the homolog of human exportin-t, mediates nuclear export of tR NA. Using fluorescence in situ hybridization, we could show that the export of some intronless tRNA species is not detectably affected by the disrupti on of LOS1. To find other factors that facilitate tRNA export, we performed a suppressor screen of a synthetically lethal los1 mutant and identified t he essential translation elongation factor eEF-1A. Mutations in eEF-1A impa ired nuclear export of all tRNAs tested, which included both spliced and in tronless species. An even stronger defect in nuclear exit of tRNA was obser ved under conditions that inhibited tRNA aminoacylation. In all cases, inhi bition of tRNA export led to nucleolar accumulation of mature tRNAs. Our da ta show that tRNA aminoacylation and eEF-1A are required for efficient nucl ear tRNA export in yeast and suggest coordination between the protein trans lation and the nuclear tRNA processing and transport machineries.