Numerous rRNA molecules form the apicomplexan mitoribosome via repurposed protein and RNA elements.
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Shikha S, Tobiasson V, Ferreira Silva M, Ovciarikova J, Beraldi D, Mühleip A, Sheiner L
Nat Commun 16 (1) 817 [2025-01-18; online 2025-01-18]
Mitochondrial ribosomes (mitoribosomes) are essential, and their function of synthesising mitochondrial proteins is universal. The core of almost all mitoribosomes is formed from a small number of long and self-folding rRNA molecules. In contrast, the mitoribosome of the apicomplexan parasite Toxoplasma gondii assembles from over 50 extremely short rRNA molecules. Here, we use cryo-EM to discover the features that enable this unusual mitoribosome to perform its function. We reveal that poly-A tails added to rRNA molecules are integrated into the ribosome, and we demonstrate their essentiality for mitoribosome formation and for parasite survival. This is a distinct function for poly-A tails, which are otherwise known primarily as stabilisers of messenger RNAs. Furthermore, while ribosomes typically consist of unique rRNA sequences, here nine sequences are used twice, each copy integrated in a different mitoribosome domain, revealing one of the mechanisms enabling the extreme mitochondrial genome reduction characteristic to Apicomplexa and to a large group of related microbial eukaryotes. Finally, several transcription factor-like proteins are repurposed to compensate for reduced or lost critical ribosomal domains, including members of the ApiAP2 family thus far considered to be DNA-binding transcription factors.
PubMed 39827269
DOI 10.1038/s41467-025-56057-9
Crossref 10.1038/s41467-025-56057-9
pmc: PMC11742926
pii: 10.1038/s41467-025-56057-9