PROCESSING OF PLANT MITOCHONDRIAL TRNA(GLY) AND TRNA(SER) IS INDEPENDENT OF RNA EDITING

The genes encoding pea and potato mitochondrial tRNA(Gly) and pea mito chondrial tRNA(Ser)(GCU) were analyzed with particular respect to thei r expression. Secondary-structure models deduced from the identical po tato and pea tRNA(Gly) gene sequences revealed A(7):C-66 mismatches in the seventh base pair at the base of the acceptor stems of both tRNAs . Sequence analyses of tRNA(Gly) cDNA clones showed that these mispair ings are not corrected by C-66 to U-66 conversions, as observed in pla nt mitochondrial tRNA(Phe). Likewise, a U-6:C-67 mismatch identified i n the acceptor stem of the pea tRNA(Ser)(GCU) is not altered by RNA ed iting to a mismatched U:U pair, which is created by RNA editing in Oen othera mitochondrial tRNA(Cys). In vitro processing reactions with the respective tRNA(Gly) and tRNA(Ser)(GCU) precursors show that such con versions 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) mismat ches in double-stranded regions of tRNAs are altered by RNA editing. A n RNA editing event in plant mitochondrial tRNAs is thus not generally indicated by the presence of a mismatch but may depend on additional parameters.