OCCURRENCE OF SILENT RNA EDITING IN CHLOROPLASTS - ITS SPECIES-SPECIFICITY AND THE INFLUENCE OF ENVIRONMENTAL AND DEVELOPMENTAL CONDITIONS

We have identified three new C-to-U RNA editing sites, one in atpF and two in atpA transcripts from tobacco chloroplasts. Two of them lead t o amino acid substitutions to restore the conserved amino acid found i n the corresponding genes of other plants. However, one editing site i n the atpA transcript was found to take place partially at the third b ase of a serine codon (CU (C) under bar to CU (U) under bar), thus not leading to an amino acid substitution. This is the first report of si lent editing in chloroplasts. The extent of silent editing depends on plastid stage and light conditions, while editing at another site (fou nd 4 nt upstream from the silent editing site) takes place constitutiv ely even in non-photosynthetic cultured cells and bleached white seedl ings grown in the presence of spectinomycin and streptomycin. In pea a nd spinach, despite a conservation in sequence, no editing at the site corresponding to the silent site in tobacco was found. This observati on suggests that the silent editing detected in this study is species- specific.