QO site deficiency can be compensated by extragenic mutations in the hinge region of the iron-sulfur protein in the bc1 complex of Saccharomyces cerevisiae.

The mitochondrial bc(1) complex catalyzes the oxidation of ubiquinol and the reduction of cytochrome (cyt) c. The cyt b mutation A144F has been introduced in yeast by the biolistic method. This residue is located in the cyt b cd(1) amphipathic helix in the quinol-oxidizing (Q(O)) site.