RNA editing in the cytochrome b locus of Oenothera berteriana mitochondria modified a number of cytidine nucleotides to uridines, mostly altering codon identities. One nucleotide alteration involved a reverse modification changing a genomic thymidine to a cytidine in the cDNA sequence. The enzymatic editing activity in higher-plant mitochondria thus appears to be able to catalyze the interconversion of pyrimidines in both directions at specific nucleotides in the mRNA template.
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Schuster et al. (1990) studied this question.