Adaptive response due to changes in gene regulation: a study with Drosophila.

In spite of the critical role of the process of adaptation in evolution, there are few detailed studies of the genotypic and molecular basis of the process. Drosophila melanogaster flies selected for increased tolerance to ethanol exhibited higher levels of alcohol dehydrogenase (alcohol:NAD+ oxidoreductase; EC 1.1.1.1) activity than unselected controls. A series of tests (electrophoresis, product inhibition, temperature stability, pH optima, substrate specificity, and Michaelis constants) gave no evidence of structural differences in the enzyme of the selected and the control flies. However, quantitative immunological assays showed that the selected flies contained significantly higher amounts of alcohol dehydrogenase. Adaptation of the selected flies to higher alcohol tolerance has most likely taken place by changes not in the structural gene locus coding for the enzyme, but by regulatory changes affecting the amount of gene product.