Ciliate mitoribosome illuminates evolutionary steps of mitochondrial translation
- Stockholm University, Sweden
Abstract
To reveal steps in the evolution of translation, we identified ciliates as a model with high coding capacity of the mitochondrial genome and characterized its mitoribosomes by cryo-EM. It revealed a 94-protein and 4-rRNA assembly with an additional protein mass of ~700 kDa on the small subunit, while the large subunit lacks 5S rRNA. The structure shows that the small subunit head is constrained, tRNA binding sites are formed by mitochondria-specific protein elements, conserved protein bS1 is excluded, and bacterial RNA polymerase binding site is blocked. We provide evidence for intrinsic protein targeting system through visualization of mitochondria-specific mL105 by the exit tunnel that would facilitate recruitment of a nascent polypeptide. Functional protein uS3m is encoded by three complementary genes from the nucleus and mitochondrion, establishing a link between genetic drift and mitochondrial translation. Finally, we reannotated nine open reading frames in the mitochondrial genome that code for mitoribosomal proteins.
Data availability
The electron density maps have been deposited into EMDB, with accession codes EMD-11032 (monosome), EMD-11033 (LSU), EMD-11034 (SSU), EMD-11035 (CP), EMD-11036 (L7/L12 stalk), EMD-11037 (head), EMD-11038 (back protuberance). The model has been deposited in the PDB, with accession code 6Z1P.
Article and author information
Author details
Funding
Ragnar Söderbergs stiftelse (M44/16)
- Alexey Amunts
Cancerfonden (2017/1041)
- Alexey Amunts
H2020 European Research Council (ERC-2018-StG- 805230)
- Alexey Amunts
Knut och Alice Wallenbergs Stiftelse (2018.0080)
- Alexey Amunts
European Molecular Biology Organization (EMBO Young Investigator Program)
- Alexey Amunts
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2020, Tobiasson & Amunts
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Ciliate mitoribosome illuminates evolutionary steps of mitochondrial translation
eLife 9:e59264.
https://doi.org/10.7554/eLife.59264
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