Mitochondrial DNA (MtDNA) with a neutral buoyant density of 1.681 g/cm3 has been isolated from unfertilized eggs of Drosophila melanogaster. This DNA is a circular molecule with an average length of 5.3 µm; it reassociates with a low C0t1/2 after denaturation, and in alkaline isopycnic centrifugation it separates into strands differing in density by 0.005 g/cm3. MtDNA isolated from purified mitochondria of unfertilized eggs or from total larval DNA melts with three distinct thermal transitions. The three melting temperature values suggest that the molecule may have three regions differing in average base composition. DNA isolated from unfertilized eggs of D. melanogaster contains approximately equal amounts of MtDNA and another DNA with a buoyant density of 1.697 g/cm3, slightly less dense than main peak DNA. The possibility that the heavier DNA fraction consists of amplified ribosomal DNA was excluded by hybridization experiments, but otherwise nothing is known of its origin or function.

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