RNA editing in an untranslated region of the Ginkgo chloroplast genome.

mRNAs in plant cell organelles can be subject to RNA editing, an RNA processing step altering the identity of single nucleotide residues. In higher plant chloroplasts, editing proceeds by C-to-U conversions at highly specific sites. All known plastid RNA editing sites are located in protein-coding regions and, typically, change the coding properties of the mRNA. To gain more insight into the evolution of editing, we have determined the molecular structure and RNA editing pattern of the psbE operon of the primitive seed plant Ginkgo biloba. We report here the identification of altogether four sites of C-to-U editing, two of which are unique to Ginkgo and have not been found in other species. Surprisingly, one of the sites is located in an intercistronic spacer, thus being the first chloroplast editing site detected outside a protein-coding region. This indicates that the plastid editing machinery can operate also in untranslated regions and without having apparent functional consequences.