Genetic Evidence for the Action of Oxathiin and Thiazole Derivatives on the Succinic Dehydrogenase System of Ustilago maydis Mitochondria

The inhibitory effect of fungitoxic derivatives of 1,4-oxathiin on substrate oxidation by the basidiomyceteUstilago maydis is diminished by a single-gene mutation (oxr ). The difference between mutant and wild type is approximately the same on the basis of inhibition of either growth and operation of the tricarboxylic acid cycle in intact cells or succinate-driven reduction of ferricyanide by mitochondrial preparations. The mutation affects the behavior of the succinic dehydrogenase system of mitochondria not only in the presence but also in the absence of the toxicant, from which it is concluded that some component of the system itself has been modified. The malonate and the antimycin A sensitivity of theoxr mutant is similar to that of the wild type but cross-resistance to thiazole derivatives is easily demonstrated.