Molecular analysis of a steroid-induced regulatory hierarchy: the Drosophila E74A protein directly regulates L71-6 transcription.

Steroid hormones orchestrate the growth and development of higher organisms by directing spatially and temporally coordinated programs of gene expression. These changes in gene activity can be visualized in Drosophila by virtue of its giant salivary gland polytene chromosomes. A small set of early puffs are induced directly by the steroid hormone ecdysone. The proteins encoded by these puffs appear to induce many late secondary-response puffs as the animal begins to undergo metamorphosis. Here we report that the ETS domain DNA-binding protein encoded by the E74A early gene directly induces L71-6 late gene transcription. We identify four strong E74A binding sites within the 5' region of L71-6 demonstrate that these sites are essential for proper L71-6 induction at puparium formation. These studies provide a direct link between a steroid-induced transcription factor and the activation of a secondary-response promoter, indicating that steroid signals in higher organisms can be transduced and amplified through regulatory hierarchies.