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Characterization of several mitochondrial variants of natural isolates of Neurospora intermedia Rieck, Anne Carolyn


A survey of natural isolates of N. intermedia revealed five variants with respect to growth phenotype. These variants showed stop-start behavior in growth tubes, sometimes never attaining the full tube length. These strains are mainly.female sterile. The stop-start phenotype was not transmitted via the male parent in any cross. In two crosses, maternal transmission was demonstrated. One strain was investigated for the presence of virus-like particles, but none were found. Cytochrome spectra show a deficiency of cytochromes a. and/or b_ relative to the amount of c. In respiration studies, the one strain tested proved to be cyanide resistant and salicyl hydroxamic acid sensitive. These characteristics are also found in extranuclear mutants of N. ovassa. However, the analogy no longer holds at the mitochondrial ribosome level. An analysis of four of the strains disclosed that three are large subunit deficient. Only small subunit deficient strains have been found among the cytoplasmic mutants of N. ovassa. Restriction enzyme analysis was also carried out on the variants. It was found that they possess additional mitochondrial DNA compared to normal N. intermedia. One Eco RI fragment of M.W. 2.4 x 10 was found to be common to all variants tested, but is not found in the normal strains. There were other DNA differences which were unique to each abnormal strain. These findings suggest that the basis for the abnormal phenotypes .is some heritable factor associated with the mitochondria.

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