DISTINCT DIFFERENCES IN THE REQUIREMENTS FOR RIBONUCLEOPROTEIN COMPLEX-FORMATION ON DIFFERENTIALLY REGULATED PRE-EDITED MESSENGER-RNAS IN TRYPANOSOMA-BRUCEI

Incubation of synthetic pre-edited mRNAs with extracts of Trypanosoma brucei mitochondria results in a family of specific, stable ribonucleo protein (RNP) complexes that can be visualized by non-denaturing gel e lectrophoresis. We compared complexes that form with a substrate corre sponding to the ATPase 6 (A6) pre-mRNA 3' region that is edited in bot h bloodstream and procyclic forms with a substrate corresponding to th e 5' end of apocytochrome b (CYb) pre-mRNA that is edited only in proc yclic (insect) forms. Four to five complexes are detected with both su bstrates and are specific since competition with homologous but not he terologous substrates prevents their formation. Formation of the CYb c omplex, however, is more sensitive to heterologous RNAs. In addition, the A6 substrate is more effective at preventing formation of CYb comp lexes than the converse. CYb complex formation is also more sensitive to divalent cation and salt concentrations and formation of one A6 com ponent has a temperature optimum of 37 degrees C while that of CYb is 27 degrees C.