Nuclear mutants of Saccharomyces cerevisiae with altered subunits 4, 5, and 6 of cytochrome oxidase.

A collection of pet mutants of Saccharomyces cerevisiae has been screened for lesions in cytochrome oxidase. Three different complementation groups have been identified to consist of strains with altered forms of subunits 4, 5, or 6 that are known to be encoded by nuclear genes. The mutant proteins cross-react with antiserum to the holoenzyme or to the individual subunits but exhibit either an increase or decrease in size. In each instance the mutation imparts a respiratory deficient phenotype which is due to reduced levels of cytochrome oxidase activity in the mitochondria. These results indicate that each of the three proteins is required either for the catalytic activity or for the assembly of functional cytochrome oxidase.