A little feat in translation: miniaturized tRNAs in nematode and arachnid mitochondria

Transfer RNAs carry a highly conserved, cloverleaf-like secondary structure, which is essential to fulfill their task as adaptor molecules in translation. However, in mitochondria of metazoans, tRNA molecules were identified that deviate from this consensus structure and lack either the D- or T-arm, or, in some extreme cases, even both arms. These deviations are predominantly found in nematodes and arachnids, where in many cases the entire set of 22 mt tRNA genes are predicted to encode for such aberrant tRNAs or where even the complete loss of tRNA genes is proposed. Due to this unusual composition, we analyzed and characterized the mt tRNA pool of one representative of both groups. We identified the whole set of mt tRNAs and reannotated several tRNAs that differ significantly from previous genome-based predictions. In some cases, the sequence reads indicate putative tRNA editing events, showing that predictions exclusively based on mitogenome data have only a limited reliability. Our data also provide first insights into the modification pattern of such hairpin-like tRNAs.