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 maxi circle) encode mRNAs that are so extensively altered hy RNA editing th at 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 t he deletion of 20 genomically encoded uridines. The fully edited trans cript 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). S even guide RNAs that can specify edited CR2 sequence have been identif ied. Steady-state levels of unedited ND9 transcripts are greater in bl oodstream than in procyclic forms, but edited ND9 mRNA is present in s imilar abundance in both life cycle stages.