TRYPANOSOMA-BRUCEI RNA EDITING - ADENOSINE NUCLEOTIDES INVERSELY AFFECT U-DELETION AND U-INSERTION REACTIONS AT MESSENGER-RNA CLEAVAGE

In the currently envisioned mechanism of trypanosome mitochondrial RNA editing, U-insertion and U-deletion cycles begin with a common kind o f gRNA-directed cleavage. However, natural, altered, and mutationally interconverted editing sites reveal that U-deletional cleavage is inef ficient without and activated by ATP and ADP, while U-insertional clea vage shows completely reverse nucleotide effects. The adenosine nucleo tides' effects appear to be allosteric and determined solely by sequen ces immediately adjacent to the anchor duplex. Both U-deletional and U -insertional cleavages are reasonably active at physiological mitochon drial ATP concentration. Notably, ATP and ADP markedly stimulate compl ete U-deletion and inhibit U-insertion reactions, reflecting their eff ects on cleavage. These plus previous results suggest that U deletion and U insertion are remarkably distinct.