Isolation and Physical Mapping of the Mitochondrial Chromosome From the Zygomycete Mucor Racemosus.

Mitochondria were isolated from Mucor racemosus and DNA was purified from these organelles by cesium chloride/ethidium bromide isopycnic centrifugation. Examination of mitochondrial DNA samples with a transmission electron microscope revealed a circular mitochondrial chromosome approximately 63.8 kbp in length. Summation of restriction fragments of mitochondrial DNA separated by agarose gel electrophoresis yielded a comparable value of 63.4 kbp for the size of the intact molecule. Electrophoretic mobility and stoichiometry were determined for restriction fragments generated using nine different restriction enzymes. A physical map was deduced from single and double digestions of mitochondrial DNA with several of the restriction enzymes. The locations of the large and small ribosomal RNA genes were mapped and found to be contained in reverse orientation within a repeated region of the mitochondrial genome. This construction yields two populations of mitochondrial DNA molecules, possibly generated through a homologous recombination mechanism