EDITING CORRECTS MISPAIRING IN THE ACCEPTOR STEM OF BEAN AND POTATO MITOCHONDRIAL PHENYLALANINE TRANSFER-RNAS

Editing is a general event in plant mitochondrial messenger RNAs, but has never been detected in a plant mitochondrial transfer RNA (tRNA). We demonstrate here the occurence of a tRNA editing event in higher pl ant mitochondria: in both bean and potato, the C encoded at position 4 in the mitochondrial tRNA(Phe)(GAA) gene is converted into a U in the mature tRNA. This nucleotide change corrects the mismatched C4-A69 ba se-pair which appears when folding the gene sequence into the cloverle af structure and it is consistent with the fact that C to U transition s constitute the common editing events affecting plant mitochondrial m essenger RNAs. The tRNA(Phe)(GAA) gene is located upstream of the sing le copy tRNA(Pro)(UGG) gene in both the potato and the bean mitochondr ial DNAs. The sequences of potato and bean tRNA(Pro)(UGG) genes are co linear with the sequence of the mature bean mitochondrial tRNA(Pro)(UG G), demonstrating that this tRNA is not edited. A single copy tRNA(Ser )(GCU) gene was found upstream of the tRNA(Phe) gene in the potato mit ochondrial DNA. A U6-U67 mismatched base-pair appears in the cloverlea f folding of this gene and is maintained in the mature potato mitochon drial tRNAser(GCU), which argues in favour of the hypothesis that the editing system of plant mitochondria can only perform C to U or occasi onally U to C changes.