Confirmation of predicted edits and demonstration of unpredicted edits in Acanthamoeba castellanii mitochondrial tRNAs.

In the amoeboid protozoon Acanthamoeba castellanii 13 of the 16 mtDNA-encoded tRNA sequences have mis-matches at one or more of the first three positions in the acceptor stem. A previous study had indicated that these mis-matches are corrected by a form of RNA editing. In the present study, the pattern of editing was further investigated by sequence analysis of both halves of the acceptor stem of 11 mtDNA-encoded tRNAs. The results confirm all of the remaining editing sites predicted on the basis of the secondary structure modelling of A. castellanii mitochondrial tRNAs, and identify two unexpected edits. We also investigated the expression and editing of transcripts of an unusual trnX gene specifying an eight-nucleotide anticodon loop sequence. Although no mature 3'-CCAOH-containing tRNAX products were detected, editing was observed in some circularized tRNAX clones. The implications of these results with respect to the mechanism of editing and the evolutionary origin of this process are discussed.