A p32 family RNA editing factor acts in mitochondrial ribosome biogenesis.

p22, a p32-family p22 homotrimer, is required for mitochondrial small ribosome (mtSSU) biogenesis in Trypanosoma brucei, and its loss reduces mitochondrial translation and oxidative phosphorylation.

• Why it matters: Mitochondrial ribosome assembly in Trypanosoma brucei depends on many factors, but how p32-family RNA editing proteins connect to mitoribosome formation and organellar function was unclear.
• What they did: The authors analyzed the earliest mtSSU precursor using genetic modifications and proteomic characterization of an immunoprecipitated assemblosome, identifying a protrusion cap made of a p22 homotrimer. They then performed functional tests showing p22 is also linked to uridine-insertion editing of the cytochrome c oxidase subunit II transcript.
• The result: Ablating p22 causes mtSSU loss and a systemic reduction in mitochondrial translation, phenocopying depletion of established mitoribosomal assembly factors and compromising oxidative phosphorylation and mitochondrial function.

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