DEGRADATION OF CYTOCHROME-OXIDASE SUBUNITS IN MUTANTS OF YEAST LACKING CYTOCHROME-C AND SUPPRESSION OF THE DEGRADATION BY MUTATION OF YME1

We have confirmed by spectral analysis that cytochrome oxidase is not present in strains of the yeast Saccharomyces cerevisiae having a prim ary deficiency in cytochrome c, and we have demonstrated by immunologi cal procedures that such strains lack the mitochondrially encoded subu nits I, II, and III of cytochrome oxidase. Furthermore, pulse-chase ex periments demonstrated that subunit II is rapidly degraded in vivo. Th is degradation can be at least partially suppressed by disruption of t he nuclear gene YME1, which encodes a putative ATP-Zn2+-dependent prot ease. We suggest that the cytochrome oxidase subunits are not properly assembled in the absence of cytochrome c, and that Yme1 and possibly other proteases degrade the unassembled mitochondrial-encoded subunits of cytochrome oxidase.