Mitochondrial Translation in Trypanosomatids
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For a long period of time, the functional properties and the very existence of mitochondrial translation in trypanosomatids remained controversial. The unusual resistance of the system to the known inhibitors of translation, such as chloramphenicol, in conjunction with the extreme hydrophobicity of the translation products appeared to be the main factors that made detection and characterization of this system so difficult. As of today, only two mitochondrial translation products have been reliably identified in Leishmania tarentolae and Trypanosoma brucei: cytochrome c oxidase subunit I (COI) and apocytochrome b (Cyb) that are encoded by nonedited and 5′-edited mRNAs, respectively. A large body of circumstantial evidence suggests that the F1F0 ATPase subunit A6 and ribosomal protein S12 are also expressed in trypanosomatid mitochondria. The issue of existence of kinetoplast-mitochondrial ribosomes has been addressed lately by the isolation of the 50S monosome particles and reconstruction of their 3D-structure using single-particle cryo-electron microscopy. The overall architecture of these particles strikingly resembles that of eubacterial ribosomes, despite profound differences in the size of ribosomal RNAs and the protein content of these two classes of ribosomes. Evidence begins to accumulate that in order to selectively achieve translation of the fully edited mRNA templates the mitoribosomes are involved in higher-order interactions with mRNA editing and polyadenylation machineries. The pentatricopeptide repeat (PPR) proteins emerge as important participants in these interactions.
KeywordsCryo-electron microscopy Leishmania tarentolae Mitochondrial translation Mitoribosome Pentatricopeptide repeat (PPR) proteins RNA editing Trypanosoma brucei
The work in the authors’ laboratories has been supported by National Institutes of Health grants AI088292 (to DAM) and GM61576 (to RKA). We thank R. Aphasizhev and L. Simpson for the critical comments on the manuscript.
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