BIOCHEMICAL AND MOLECULAR CONSEQUENCES OF MASSIVE MITOCHONDRIAL GENE LOSS IN DIFFERENT TISSUES OF A MUTANT STRAIN OF DROSOPHILA-SUBOBSCURA

In the studied mutant strain of Drosophila subobscura, 78% of the mito chondrial genomes lost > 30% of the coding region by deletion, The mut ations was genetically stable, Despite this massive loss of mitochondr ial genes, the mutant did not seem to be affected, Distribution of the two genome types, cell levels of mitochondrial DNA, steady-state conc entrations of the mitochondrial gene transcripts, mitochondrial enzyma tic activities, and ATP synthesis capacities were measured in the head , thorax, and abdomen fractions of the mutant strain in comparison wit h a wild type strain, Results indicate that the deleted genomes are de tected in all fractions but to a lesser extent in the male and female abdomen, In all fractions, there is a 50% increase in cellular mitocho ndrial DNA content, Although there is a decrease in steady-state conce ntrations of mitochondrial transcripts of genes affected by deletion, this is smaller than expected, The variations in mitochondrial biochem ical activities in the different fractions of the wild strain are uphe ld in the mutant strain, Activity of complex I (involved in mutation) nevertheless shows a decrease in all fractions; activity of complex II I (likewise involved) shows little or no change; finally, mitochondria l ATP synthesis capacity is identical to that observed in the wild str ain, This latter finding possibly accounts for the lack of phenotype, This mutant is a good model for studying mitochondrial genome alterati ons and the role of the nuclear genome in these phenomena.