A post-transcriptional respiratome regulon in trypanosomes

Post-transcriptional regulons coordinate the expression of groups of genes in eukaryotic cells, yet relatively few have been characterised. Parasitic trypanosomatids are particularly good models for studies on such mechanisms because they exhibit almost exclusive polycistronic, and unregulated, transcription. Here, we identify the Trypanosoma brucei ZC3H39/40 RNA-binding proteins as regulators of the respiratome; the mitochondrial electron transport chain (complexes I-IV) and the FoF1-ATP synthase (complex V). A high-throughput RNAi screen initially implicated both ZC3H proteins in variant surface glycoprotein (VSG) gene silencing. This link was confirmed and both proteins were shown to form a cytoplasmic ZC3H39/40 complex. Transcriptome and mRNA-interactome analyses indicated that the impact on VSG silencing was indirect, while the ZC3H39/40 complex specifically bound and stabilised transcripts encoding respiratome-complexes. Quantitative proteomic analyses revealed specific positive control of respiratome protein abundance. Our findings establish a link between the mitochondrial respiratome and VSG gene silencing. They also reveal a major respiratome regulon controlled by the conserved trypanosomatid ZC3H39/40 RNA-binding proteins.