Evidence for import of a lysyl-tRNA into marsupial mitochondria

The mitochondrial tRNA gene for lysine was analyzed in 11 different marsupi al mammals. Whereas its location is conserved when compared with other vert ebrate mitochondrial genomes, its primary sequence and inferred secondary s tructure are highly unusual and variable. For example, eight species lack t he expected anticodon. Because the corresponding transcripts a-re not alter ed by any RNA-editing mechanism, the lysyl-tRNA gene seems to represent a m itochondrial pseudogene. Purification of marsupial mitochondria, and in vit ro aminoacylation of isolated tRNAs with lysine, followed by analysis of am inoacylated tRNAs, show that a nuclear-encoded tRNA(Lys) is associated with marsupial mitochondria. We conclude that a functional tRNA(Lys) encoded in the nuclear genome is imported into mitochondria in marsupials. Thus, tRNA import is not restricted to plant, yeast, and protozoan mitochondria but a lso occurs also in mammals.