A SINGLE EDITING EVENT IS A PREREQUISITE FOR EFFICIENT PROCESSING OF POTATO MITOCHONDRIAL PHENYLALANINE TRANSFER-RNA

In bean, potato, and Oenothera plants, the C encoded at position 4 (C- 4) in the mitochondrial tRNA(GAA)(Phe) gene is converted into a U in t he mature tRNA, This nucleotide change corrects a mismatched C-4-A(69) base pair which appears when the gene sequence is folded into the clo verleaf structure. C-to-U conversions constitute the most common editi ng events occurring in plant mitochondrial mRNAs. While most of these conversions introduce changes in the amino acids specified by the mRNA and appear to be essential for the synthesis of functional proteins i n plant mitochondria, the putative role of mitochondrial tRNA editing has not yet been defined. Since the edited form of the tRNA has the co rrect secondary and tertiary structures compared with the nonedited fo rm, the two main processes which might be affected by a nucleotide con version are aminoacylation and maturation. To test these possibilities , we determined the aminoacylation properties of unedited and edited p otato mitochondrial tRNA(Phe) in vitro transcripts, as well as the pro cessing efficiency of in vitro-synthesized potato mitochondrial tRNA(P he) precursors. Reverse transcription-PCR amplification of natural pre cursors followed by cDNA sequencing was also used to investigate the i nfluence of editing on processing. Our results show that C-to-U conver sion at position 4 in the potato mitochondrial tRNA(GAA)(Phe) is not r equired for aminoacylation,vith phenylalanine but is likely to be esse ntial for efficient processing of this tRNA.