Processing of plant mitochondrial tRNAGly and tRNASer(GCU) is independent of RNA editing

The genes encoding pea and potato mitochondrial tRNAGly and pea mitochondrial tRNASer(GCU) were analyzed with particular respect to their expression. Secondary-structure models deduced from the identical potato and pea tRNAGly gene sequences revealed A7:C66 mismatches in the seventh base pair at the base of the acceptor stems of both tRNAs. Sequence analyses of tRNAGly cDNA clones showed that these mispairings are not corrected by C66 to U66 conversions, as observed in plant mitochondrial tRNAPhe. Likewise, a U6:C67 mismatch identified in the acceptor stem of the pea tRNASer(GCU) is not altered by RNA editing to a mismatched U:U pair, which is created by RNA editing in Oenothera mitochondrial tRNACys. In vitro processing reactions with the respective tRNAGly and tRNASer(GCU) precursors show that such conversions are not necessary for 5′ and 3′ end maturation of these tRNAs. These results demonstrate that not all C:A (A:C) or U:C (C:U) mismatches in double-stranded regions of tRNAs are altered by RNA editing. An RNA editing event in plant mitochondrial tRNAs is thus not generally indicated by the presence of a mismatch but may depend on additional parameters.