MITOCHONDRIAL GENOME OF THE DIMORPHIC ZYGOMYCETE MUCOR-RACEMOSUS

Mitochondria were isolated from the dimorphic zygomycete Mucor racemos us by differential centrifugation. DNA from the organelles was purifie d by cesium chloride-ethidium bromide isopycnic centrifugation. Examin ation of the mitochondrial DNA by electron microscopy revealed a circu lar chromosome approximately 63.8 kbp in circumference. The chromosome was digested with restriction endonucleases and the resulting DNA fra gments were separated by agarose-gel electrophoresis. Electrophoretic mobilities and stoichiometry of the fragments indicated a mixed popula tion of mtDNA molecules each with a size of about 63.4 kbp. Physical m aps were constructed from analyses of fragments generated in single an d double restriction digests and from the hybridization of fragments t o probes for the large and small mitochondrial rRNA genes from Sacchar omyces cerevisiae. The Mucor mitochondrial chromosome was found to exi st in the form of two flip-flop isomers with inverted repeat sequences encoding both rRNA genes.