THE MITOCHONDRIAL GENOMES OF USTILAGO-CYNODONTIS AND ACANTHAMOEBA-CASTELLANII

Mitochondrial DNA from U. cynodontis was investigated. Its dG + dC [guanine + cytosine] content is equal to 33.5%; its buoyant density (1.698 g/cm3) is higher, by 5 mg/cm3, and its melting temperature (82.5.degree. C) is lower than expected for a bacterial DNA having the same base compositions. The 1st derivative of the melting curve of the DNA of U. cynodontis indicates a large compositional heterogeneity. The molarity of elution from hydroxyapatite is high, 0.28 M phosphate, allowing its partial separation from nuclear DNA. Degradation by micrococcal nuclease indicates that about 25% of the DNA is formed by stretches having no more than 15% dG + dC. The unit size of mitochondrial genome is about 50 .times. 106. In most of its properties, the mitochondrial genome of U. cynodontis presents strong analogies with that of Saccharomyces cerevisiae. A parallel investigation on mitochondrial DNA from A. castellani, which has as genome unit size of only 27 .times. 106, showed that this shares with the former the dG + dC content (32.9%), the melting temperature (82.5.degree. C), a large compositional heterogeneity and a very similar pattern of micrococcal nuclease degradation. The buoyant density (1.692 g/cm3) and the molarity of elution from hydroxyapatite (0.25 M phosphate) are normal, probably because of a different short-sequence pattern and the fact that the dA + dT-rich stretches of A. castellanii are shorter, on the average.