DIRECT VISUALIZATION OF URIDYLATE DELETION IN-VITRO SUGGESTS A MECHANISM FOR KINETOPLASTID RNA EDITING

Deletion of uridylates from the 3'-most editing site of synthetic ATPa se 6 pre-mRNA can be visualized directly by coincubation of a radiolab eled substrate RNA and a synthetic gRNA in 20S fractions of T. brucei mitochondrial lysates. Substrate RNA cleavage is gRNA directed and occ urs 3' to the uridylates to be deleted. U residues appear to be sequen tially removed from the 3' end of the 5' cleavage product prior to rel igation of the two pre-mRNA halves. gRNA/mRNA chimeric molecules are a lso produced. Time course experiments indicate that chimeras appear af ter cleavage intermediates and edited product. Furthermore, a mutant g RNA promotes formation of edited product but not detectable chimeras. Our results suggest a model for kinetoplastid RNA editing in which chi meric molecules are nonproductive end products of editing and not inte rmediates that serve as a repository for deleted U's.