Editing of the wheat coxIII transcript: evidence for twelve C to U and one U to C conversions and for sequence similarities around editing sites.

The complete cDNA sequence corresponding to the wheat coxIII gene transcript (coding for subunit 3 of cytochrome oxidase) has been determined by a method involving cDNA synthesis using specific oligonucleotides as primers followed by PCR amplification, cloning and sequencing of the amplification products. In 12 different clones, the same 13 nucleotide modifications have been found as compared to the genomic mitochondrial DNA sequence. Among these modifications, 12 are C----U conversions which change codons identities, thereby increasing the homology between the wheat COXIII protein and the corresponding protein of non-plant organisms. The 13th modification is a silent U----C conversion which seems to be an unfrequent editing eventin plant mitochondria. Homologies can be found between sequences surrounding editing sites in the coxIII transcript and in other wheat mitochondrial transcripts. The presence of such homology suggests that these sequences could base-pair with a common RNA molecule which might be involved in editing site recognition.