The final cut

To generate functional tRNA molecules, precursor RNAs must undergo several processing steps. While the enzyme that generates the mature tRNA 5′‐end, RNase P, has been thoroughly investigated, the 3′‐processing activity is, despite its importance, less understood. While nothing is known about tRNA 3′‐processing in archaea, the phenomenon has been analysed in detail in bacteria and is known to be a multistep process involving several enzymes, including both exo‐ and endonucleases. tRNA 3′‐end processing in the eukaryotic nucleus seems to be either exonucleolytic or endonucleolytic, depending on the organism analysed, whereas in organelles, 3′‐end maturation occurs via a single endonucleolytic cut. An interesting feature of organellar tRNA 3′‐processing is the occurrence of overlapping tRNA genes in metazoan mitochondria, which presents a unique challenge for the mitochondrial tRNA maturation enzymes, since it requires not only the removal but also the addition of nucleotides by an editing reaction.