Characterization of cytochrome c oxidase III transcripts that are edited only in the 3' region

The cytochrome c oxidase subunit III (COIII) transcript of T. brucei is extensively edited by the addition and deletion of uridines. We have identified partially edited COIII RNAs; they have unedited 5' and edited 3' regions. Transcripts with edited 5' but unedited 3' regions were not detected. The partially edited RNAs may be editing intermediates. The junctions of unedited and edited sequences in cDNAs differ from both the DNA and fully edited mRNA sequences over a multinucleotide region. The partially edited RNAs could arise from several processes, but it seems likely that editing proceeds in the 3' to 5' direction.