Insight into the interactions between subunits I and II of the cytochrome c oxidase of the yeast Saccharomyces cerevisiae by means of extragenic complementation.

In yeast, revertants were selected from two respiratory deficient mutants carrying mutations in the catalytic subunits of cytochrome oxidase. From a mutant carrying a double mutation in the vicinity of the copper binding pocket in subunit II, two genetically independent revertants were obtained in which the same extragenic reversion mutation was observed, A147V, in the putative helix 4 of subunit I. A comparison with revertants derived from the second deficient mutant, carrying the deficiency mutation, S140L, in the loop 3-4 of subunit I, provides additional data in favour of an interaction between helix 4 of subunit I and subunit II.