EXTENSIVE EDITING OF CR-2 MAXICIRCLE TRANSCRIPTS OF TRYPANOSOMA-BRUCEI PREDICTS A PROTEIN WITH HOMOLOGY TO A SUBUNIT OF NADH DEHYDROGENASE

Several genes of the Trypanosoma brucei mitochondrial genome (the maxicircle) encode mRNAs that are so extensively altered hy RNA editing that the gene cannot be identified by analysis of the DNA sequence. The 322-nucleotide preedited RNA of one of these genes, CR2, is converted into a 647-nucleotide transcript by the addition of 345 uridines and the deletion of 20 genomically encoded uridines. The fully edited transcript has an open reading frame that predicts a 194-amino-acid protein. This protein, which we name ND9 (NADH dehydrogenase subunit 9), has homology to a subunit of NADH dehydrogenase (respiratory complex I). Seven guide RNAs that can specify edited CR2 sequence have been identified. Steady-state levels of unedited ND9 transcripts are greater in bloodstream than in procyclic forms, but edited ND9 mRNA is present in similar abundance in both life cycle stages.