CREATION OF AN INITIATION CODON BY RNA EDITING IN THE COXI TRANSCRIPTFROM TOMATO MITOCHONDRIA

Nucleotide-sequence analysis showed that the gene for cytochrome oxida se subunit I (coxI) from tomato mitochondrial DNA has an ACG codon at a conserved position corresponding to an ATG initiation codon in other higher-plant coxI genes. cDNA-sequence analysis of the coxI transcrip ts showed that 15 positions in the genomic DNA were converted from C t o U in the transcripts by RNA editing. One of the editing events is ob served at the indicated ACG codon, producing an ATG initiation codon. The nucleotide sequences of 37 cDNA clones showed that the initiation codon was created in 32 out of the 37 clones, while nucleotide positio ns 254 and 11 were edited in 37 and 34 of the 37 clones examined, resp ectively, suggesting that creation of the initiation codon is a post-t ranscriptional event, The BamHI site at nucleotide position 757-762 wi thin the coxI genomic DNA was altered in all 97 cDNA clones examined, demonstrating that RNA editing at this site in the transcripts is very common. RNA editing takes place to a lesser extent at the initiation codon, compared with editing at internal position 254. This indicates that editing is either a random process or that it involves a mechanis m favoring less RNA editing in the initiation codon than in internal s ites.