Unusual usage of wobble modifications in mitochondrial tRNAs of the nematode Ascaris suum

To understand the decoding property of nematode mitochondrial tRNAs with unusual secondary structures, post-transcriptional modifications at wobble positions of Ascaris suum mitochondrial tRNAs corresponding to two-codon families ending with a purine were analyzed. 5-Carboxymethylaminomethyluridine (cmnm5U) was identified at the wobble positions of tRNALys, tRNAGlu and tRNAGln, while 5-carboxymethylaminomethyl-2-thiouridine (cmnm5s2U) was present in tRNAUAALeuandtRNATrp. In most bacterial and mitochondrial tRNAs, the 2-thiouridine derivative is present in tRNAs for Lys, Glu and Gln. These is no report that cmnm5s2U is used in tRNAUAALeuandtRNATrp. The unusual usage of wobble modifications might assist decoding of nematode mitochondrial mRNAs.