Stable heteroplasmy for a large-scale deletion in the coding region of Drosophila subobscura mitochondrial DNA.

Due to the extremely economic organization of the animal mitochondrial genome, large-scale deletions are rarely found in animal mtDNA. We report the occurrence of a massive deletion in the coding region of mtDNA in Drosophila subobscura. Restriction mapping and nucleotide sequence analysis revealed that the deletion encompasses six protein genes and four tRNAs. All individuals of an isofemale strain proved to be heteroplasmic for normal and deficient mtDNA molecules. This type of heteroplasmy resembles one observed in patients with mitochondrial myopathies but differs in that the fitness of heteroplasmic flies is not significantly reduced even though the mutant mtDNA constitutes 50-80% of total mtDNA in most of the individuals studied. The heteroplasmic strain is genetically stable: despite extensive screening not a single homoplasmic fly was observed since the foundation of the line.