Genetic information in chloroplast DNA is sometimes altered at the transcript level by a process known as RNA editing. Sequence analysis of amplified cDNAs for 69 potential editing sites revealed 13 real editing sites in transcripts of 11 tobacco chloroplast genes. Together with those reported previously, these bring the total of edited sites observed in tobacco chloroplast transcripts to 31 (all involve C to U conversion). Alignment of sequences around the 31 editing sites revealed no obvious consensus, apart from an apparent bias for U or C at position -1 and A at position +2. Editing in tobacco rpoA mRNA restores the conserved leucine residue which is known to be important for transcriptional activation of the alpha subunit of E. coli RNA polymerase. Editing of this site is partial and the extent of editing depends on developmental conditions, suggesting that editing is, at least in part, involved in the regulation of chloroplast-encoded RNA polymerase activity.