KRGG1 function in RNA editing in Trypanosoma brucei

Mitochondrial gene expression in trypanosomes requires numerous multiprotein complexes that are unique to kinetoplastids. Among these, the most well characterized are RNA editing catalytic complexes (RECCs) that catalyze the guide RNA (gRNA)-specified insertion and deletion of uridines during mitochondrial mRNA maturation. This post-transcriptional resequencing of mitochondrial mRNAs can be extensive, involving dozens of different gRNAs and hundreds of editing sites with most of the mature mRNA sequences resulting from the editing process. Proper coordination of the editing with the cognate gRNAs is attributed to RNA editing substrate-binding complexes (RESCs), which are also required for RNA editing. Although the precise mechanism of RESC function is less well understood, their affinity for binding both editing substrates and products suggests that these complexes may provide a scaffold for RECC catalytic processing. KRGG1 has been shown to bind RNAs, and although affinity purification co-isolates RESC complexes, its role in RNA editing remains uncertain. We show here that KRGG1 is essential in BF parasites and required for normal editing. KRGG1 repression results in reduced amounts of edited A6 mRNA and increased amounts of edited ND8 mRNA. Sequence and structure analysis of KRGG1 identified a region of homology with RESC6, and both proteins have predicted tandem helical repeats that resemble ARM/HEAT motifs. The ARM/HEAT-like region is critical for function as exclusive expression of mutated KRGG1 results in growth inhibition and disruption of KRGG1 association with RESCs. These results indicate that KRGG1 is critical for RNA editing and its specific function is associated with RESC activity.