A novel type of RNA editing occurs in the mitochondrial tRNAs of the centipede Lithobius forficatus

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Abstract
We determined the complete mtDNA sequence of the centipede Lithobius forficatus and found that only one of the 22 inferred tRNA genes encodes a fully paired aminoacyl acceptor stem. The other 21 genes encode tRNAs with up to five mismatches in these stems, and some of these overlap extensively with the downstream genes. Because a well-paired acceptor stem is required for proper tRNA functioning, RNA editing in the products of these genes was suspected. We investigated this hypothesis by studying cDNA sequences from eight tRNAs and found the editing of up to 5 nt at their 3′ ends. This editing appears to occur by a novel mechanism with the 5′ end of the acceptor stem being used as a template for the de novo synthesis of the 3′ end, presumably by an RNA-dependent RNA polymerase. In addition, unusual secondary structures for several tRNAs were found, including those lacking a TΨC (T) or a dihydrouridine (D) arm, and having an unusual number of base pairs in the acceptor or anticodon stems.