Abeer Prakash Singh

Abstract Mitochondrial gene expression needs to be balanced with cytosolic translation to produce oxidative phosphorylation complexes. In yeast, translational feedback loops involving lowly expressed proteins called translational activators help to achieve this balance. Synthesis of cytochrome b (Cytb or COB), a core subunit of complex III in the respiratory chain, is controlled by three translational activators and the assembly factor Cbp3-Cbp6.

Highlights • Proximity labeling of proteins shows connectivity of mitochondrial gene expression • Interactors at the mRNA channel entrance and exit support translation initiation • Polypeptide tunnel exit serves as a platform to organize OXPHOS assembly factors • Synthesis of Cox1 is directly coupled to co-factor acquisition and early assembly Summary Mitochondria contain their own gene expression systems, including membrane-bound ribosomes dedicated to synthesizing a few hydrophobic subunits...

Highlights • Translational feedback regulation in mitochondria involves a molecular rheostat • Alternate binding of two translational activators to the ribosomal tunnel exit • Ribosomal binding of Cbs1 sequesters COB mRNA to repress translation • Cbp3-Cbp6 liberated during assembly replaces Cbs1 for translational activation Summary The mitochondrial oxidative phosphorylation system comprises complexes assembled from subunits derived from mitochondrial and nuclear gene expression.