RNA binding proteins MRP1 (gBP21) and MRP2 (gBP25) are essential for editing and stability of a subset of mitochondrial mRNAs in procyclic Trypanosoma brucei

Abstract

In trypanosomes, MRP1 and MRP2 (previously called gBPx and gBPy, in which x and y indicate the MW of these proteins in a particular species) are guide (g)RNA binding proteins that are part of a large heteromeric complex that may play a role in U‐insertion/deletion editing of mitochondrial mRNAs. In order to shed more light on the function of these proteins, we generated procyclic Trypanosoma brucei cell lines in which the levels of MRP 1 and/or MRP2 mRNA were downregulated by RNA interference (RNAi). Here we report that the RNAi‐mediated knockdown of MRP1 and/or MRP2 resulted in severe growth inhibition and loss of both proteins. This loss occurred even in cells in which only one of the MRPs was targeted by RNAi, indicating a mutual dependence for stability of these proteins. The elimination of the MRPs substantially reduced the levels of edited cytB and RPS12 mRNAs, but resulted in little or no reduction of edited cox2, cox3 and A6 mRNAs, as measured in poisoned primer extension analyses. Surprisingly, we found a five‐fold increase in ND7 mRNA editing in MRP1+2 double knockdown cells. In addition, the knockdowns also resulted in reduction in the amounts of mRNAs that do not undergo RNA editing (cox1, ND4 and ND5 mRNAs), but little change was observed for mitoribosomal 12S rRNA. Together, the results indicate that in procyclic T. brucei, MRP1 and MRP2 play a role in transcript‐specific editing and other RNA processing activities.