MITOCHONDRIAL GENOME OF THE DIMORPHIC ZYGOMYCETE MUCOR-RACEMOSUS

Mitochondria were isolated from the dimorphic zygomycete Mucor racemosus by differential centrifugation. DNA from the organelles was purified by cesium chloride-ethidium bromide isopycnic centrifugation. Examination of the mitochondrial DNA by electron microscopy revealed a circular chromosome approximately 63.8 kbp in circumference. The chromosome was digested with restriction endonucleases and the resulting DNA fragments were separated by agarose-gel electrophoresis. Electrophoretic mobilities and stoichiometry of the fragments indicated a mixed population of mtDNA molecules each with a size of about 63.4 kbp. Physical maps were constructed from analyses of fragments generated in single and double restriction digests and from the hybridization of fragments to probes for the large and small mitochondrial rRNA genes from Saccharomyces cerevisiae. The Mucor mitochondrial chromosome was found to exist in the form of two flip-flop isomers with inverted repeat sequences encoding both rRNA genes.