cis Recognition elements in plant mitochondrion RNA editing

RNA editing in higher plant mitochondria modifies mRNA sequences by means of C-to-U conversions at highly specific sites. To determine the cis elements involved in recognition of an editing site in plant mitochondria, deletion and site-directed mutation constructs containing the cognate cox II mitochondrial gene were introduced into purified mitochondria by electroporation. The RNA editing status was analyzed for precursor and spliced transcripts from the test construct. We found that only a restricted number of nucleotides in the vicinity of the target C residue were necessary for recognition by the editing machinery and that the nearest neighbor 3' residues were crucial for the editing process. We provide evidence that two functionally distinguishable sequences can be defined: the 16-nucleotide 5' region, which can be replaced with the same region from another editing site, and a 6-nucleotide 3' region specific to the editing site. The latter region may play a role in positioning the actual editing residue.