Yeast ubiquinol: cytochrome c oxidoreductase is still active after inactivation of the gene encoding the 17‐kDa subunit VI

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Abstract
The single nuclear gene encoding the 17‐kDa subunit VI of yeast ubiquinol: cytochrome c oxidoreductase has been inactivated by one‐step gene disruption. Disruption was verified by Southern blot analysis of nuclear DNA and immunoblotting. Cells lacking the 17‐kDa protein are still capable of growth on glycerol and they contain all other subunits of complex III at wild‐type levels, implying that the 17‐kDa subunit is not essential for either assembly of complex III, or its function. In vitro, electron transport activity of complex III of mutant cells is about 40% of the wild‐type complex, but for the total respiratory chain no significant difference in activity was measured between mutant and wild type. The energy‐transducing capacity of the complex is not reduced in the absence of the 17‐kDa protein. In a relatively high proportion of the transformants, disruption of the 17‐kDa gene was accompanied by the appearance of a second mutation causing a petite phenotype. In these cells which lack cytochrome b, the presence of the 17‐kDa protein (after complementation) results in stabilization of cytochrome c1.