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-encod ed tRNA sequences have mis-matches at one or more of the first three positi ons in the acceptor stem. A previous study had indicated that these mis-mat ches are corrected by a form of RNA editing. In the present study, the patt ern of editing was further investigated by sequence analysis of both halves of the acceptor stem of ii mtDNA-encoded tRNAs. The results confirm all of the remaining editing sites predicted on the basis of the secondary struct ure modelling of A. castellanii mitochondrial tRNAs, and identify two unexp ected edits. We also investigated the expression and editing of transcripts of an unusual trnX gene specifying an eight-nucleotide anticodon loop sequ ence. Although no mature 3'-CCA(OH)-containing tRNA(X) products were detect ed, editing was observed in some circularized tRNAX clones. The implication s of these results with respect to the mechanism of editing and the evoluti onary origin of this process are discussed.