Organization of minicircle genes for guide RNAs in Trypanosoma brucei.

We have identified four T. brucei minicircle sequences that are complementary to cytochrome oxidase III (COIII) edited mRNA sequence and have shown the existence of transcripts from three of these minicircle sequences. These minicircle transcripts potentially serve as guide RNAs (gRNAs) for RNA editing of the COIII transcript. These gRNAs range in size from 55 to 70 nucleotides, are heterogeneous in sequence, and have a 5' terminal triphosphate. The genes for these gRNAs are flanked by imperfect 18 bp repeats separated by approximately 110 bp. Transcription initiates at the first purine within a conserved sequence, 5'-RYA-YA-3', 31 or 32 bp from the upstream inverted repeat. We propose that these 18 bp inverted repeats are important for minicircle gRNA expression in T. brucei.