RNA editing changes the identity of a mitochondrial tRNA in marsupials

In the mitochondrial genome of marsupials, the tRNA gene located at the position where in other mammals an aspartyl-tRNA is encoded carries the glycine anticodon GCC. Post-transcriptionally, an RNA editing mechanism affects the second position of the anticodon such that the aspartate anticodon GUC is created in approximately 50% of the mature tRNA pool. We show that the unedited version of this tRNA'Asp' (GCC) can be specifically aminoacylated with glycine in vitro, while the edited version becomes aminoacylated with aspartic acid. Furthermore, we show that both forms are aminoacylated to a substantial extent in vivo. By replacing an amino group with a keto group, RNA editing thus changes the identity of this tRNA allowing a single gene to encode two tRNAs.