The cytochromebc1 complex of the yeastSaccharomyces cerevisiae is composed of 10 different subunits that are assembledas a symmetrical dimer in the innermitochondrial membrane. Three of the subunits contain redox centers and participate in catalysis, whereas little is known about the function of the seven supernumerary subunits. To gain fur-ther insight into the function of the supernumerary subunits in the assembly process, we have examined the subunit composition of mitochondrial membranes isolated from yeast mutants in which the genes for supernumerary sub-units and cytochromeb were deleted and from yeast mutants containing double deletions of supernumerary subunits. .
