MAXICIRCLE GENOMIC ORGANIZATION AND EDITING OF AN ATPASE SUBUNIT-6 RNA IN TRYPANOSOMA-CRUZI

The DNA sequence of a 5736-nucleotide (nt) Trypanosoma cruzi maxicircl e fragment was determined. Sequence comparisons indicate that its 5' t erminus is the homologue of the downstream portion of the NADH dehydro genase subunit 7 gene and that its 3' region is homologous to the maxi circle unidentified reading frame II gene. The region between these tw o gene segments contains six additional genes that encode mitochondria l proteins, including ATPase subunit 6 (A6). Comparison of the A6 maxi circle DNA sequence with that of an A6 cDNA indicates that the A6 RNA is extensively edited throughout its length. A 49-nt sequence that cou ld serve as template for transcription of a guide RNA for editing a se gment of the A6 RNA was found in one of 24 minicircle variable regions sequenced. Moreover, the presence of an RNA having this sequence was demonstrated in an RNAse protection assay. This is the first identific ation of a guide RNA template in a T. cruzi minicircle. Taken together , our findings suggest that T, cruzi and Trypanosoma brucei brucei are phylogenetically closer to each other than they are to Leishmania tar entolae, despite the relative similarity of the life cycles of the lat ter and T. cruzi.