Mitochondrial translation factors of T rypanosoma brucei: elongation factor‐ Tu has a unique subdomain that is essential for its function

Summary Mitochondrial translation in the parasitic protozoan T rypanosoma brucei relies on imported eukaryotic‐type tRNAs as well as on bacterial‐type ribosomes that have the shortest known rRNAs . Here we have identified the mitochondrial translation elongation factors EF ‐ Tu , EF ‐ Ts , EF ‐ G 1 and release factor RF 1 of trypanosomatids and show that their ablation impairs growth and oxidative phosphorylation. In vivo labelling experiments and a SILAC ‐based analysis of the global proteomic changes induced by EF ‐ Tu RNAi directly link EF ‐ Tu to mitochondrial translation. Moreover, EF ‐ Tu RNAi reveals downregulation of many nuclear encoded subunits of cytochrome oxidase as well as of components of the bc1‐complex, whereas most cytosolic ribosomal proteins were upregulated. Interestingly, T . brucei   EF ‐ Tu has a 30‐amino‐acid‐long, highly charged subdomain, which is unique to trypanosomatids. A combination of RNAi and complementation experiments shows that this subdomain is essential for EF ‐ Tu function, but that it can be replaced by a similar sequence found in eukaryotic EF ‐1a, the cytosolic counterpart of EF ‐ Tu . A recent cryo‐electron microscopy study revealed that trypanosomatid mitochondrial ribosomes have a unique intersubunit space that likely harbours the EF ‐ Tu binding site. These findings suggest that the trypanosomatid‐specific EF ‐ Tu subdomain serves as an adaption for binding to these unusual mitochondrial ribosomes.