The genomic complexity of Acanthamoeba castellanii mitochondrial DNA

1 DNA of DNase-treated mitochondria of Acanthamoeba castellanii bands at a buoyant density of 1.690 g/cm3. Up to 80% of the molecules were circular, with a circumference of 12.7 μm. Two circular conformations, the closed twisted and the open form, were separated in preparative CsCl–ethidium bromide gradients. 2 When mtDNA was renatured at a temperature Tm– 23°C, deviations from second-order kinetics were observed. At Tm– 10°C, however, it renatured as a single kinetic class without indications of sequence repetition. The coincidence of the kinetic complexity (2.57 × 107) and the circle contour length within the limits of error of the methods suggests that each circular molecule represents a chondriome. 3 The main DNA component, which is of nuclear origin and has a peak density of 1.716 g/cm3 in CsCl, displays heterophasic renaturation kinetics. Its slow-reassociating fraction shows a kinetic complexity corresponding to a molecular weight of 2.1 × 1010. Approximately 22% of the main component appears to be repetitive at a renaturation temperature of Tm– 23°C.