Towards a mechanistic understanding of RNA processing machines

Trypanosomatid parasites constitute a huge health and economic burden in developing countries. These organisms edit essential mitochondrial mRNAs using a unique and fascinating RNA-editing mechanism not present in mammals. As such, the RNA-editing machinery is an attractive target for development of antiparasitic drugs. During mRNA editing, “guide” RNAs direct uridine insertion or deletion within a large protein complex: the core editosome. How RNA substrates are recognised by this molecular machine is poorly understood. Remarkably, no RNA is stably associated with the editosome; instead peripheral proteins and their RNA complexes ensure efficient editing. These ancillary complexes generate guide RNAs, anneal them to pre-mRNAs, enable multiple rounds of mRNA editing within the core editosome and conduct post-editing maturation of mRNA. Using combined structural, biochemical and cell-based approaches we will address key mechanistic questions for trypanosome mRNA editing. We will elucidate the structural basis for strand-specific mRNA cleavage and mRNA re-ligation; how oligouridylylated transcripts are recognised and how these sequences might direct transcript stabilisation or degradation. This work will both illuminate how RNA substrates are recognised on core editing enzymes to facilitate drug discovery and inform our understanding of oligouridylylation-directed RNA processing, which important in mammalian gene expression.