RNA editing in an untranslated region of the Ginkgo chloroplast genome

mRNAs in plant cell organelles can be subject to RNA editing, an RNA proces sing step altering the identity of single nucleotide residues. In higher pl ant chloroplasts, editing proceeds by C-to-U conversions at highly specific sites. All known plastid RNA editing sites are located in protein-coding r egions and, typically, change the coding properties of the mRNA. To gain mo re 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 s ites 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 in tercistronic spacer, thus being the first chloroplast editing site detected outside a protein-coding region. This indicates that the plastid editing m achinery can operate also in untranslated regions and without having appare nt functional consequences. (C) 1999 Elsevier Science B.V. All rights reser ved.