The yeast tRNACUU Lys is transcribed from a nuclear gene and then unequally redistributed between the cytosol (97–98%) and mitochondria (2–3%). We have optimized the conditions for its specific import into isolated mitochondria. However, only a minor fraction (about 0.5%) of the added tRNA was translocated into the organelles. An in vitro transcript, once aminoacylated, appeared to be a better import substrate than the natural tRNA which carries modified nucleosides. The tRNA is translocated across mitochondrial membranes in its aminoacylated form and remains relatively stable inside the organelle. Possible roles of aminoacylation, tRNA-protein interactions and nucleoside modification in subcellular partitioning of the tRNA are discussed.
