Identification of cytochrome c oxidase subunits in nuclear yeast mutants lacking the functional enzyme.

Yeast mutants specifically lacking cytochrome c oxidase activity were screened for cytochrome c oxidase subunits by one- and two-dimensional electrophoresis, electrophoresis in exponential gradient gels, and immunoprecipitation with antisera against one or more of the cytoplasmically made subunits of the enzyme. Two cytochrome c oxidase-less nuclear mutants previously described from this laboratory each lack one or more mitochondrially synthesized cytochrome c oxidase subunits while possessing all four cytoplasmically synthesized subunits of that enzyme. The subunits remaining in these mutants were not assembled with each other; the cytoplasmically made subunits IV and VI could be released from the mitochondria by sonic oscillation, in contrast to the situation in wild type cells. No electrophoretically detectable alterations were found in any of the cytochrome c oxidase subunits present in the mutants. Nuclear mutations may thus cause both a loss as well as a defective assembly of mitochondrially made cytochrome c oxidase subunits.