The [PSI] prion modulates cytochrome oxidase deficiency caused by deletion of .

Cytochrome oxidase (CcO) is a pivotal enzyme of the mitochondrial respiratory chain, which sustains bioenergetics of eukaryotic cells. Cox12, a peripheral subunit of CcO oxidase, is required for full activity of the enzyme, but its exact function is unknown. Here experimental evolution of a Δ strain for ∼300 generations allowed to restore the activity of CcO oxidase.