Molecular interactions within the ecdysone regulatory hierarchy: DNA binding properties of the Drosophila ecdysone-inducible E74A protein.

The E74 early ecdysone-inducible gene plays a key role in the regulatory hierarchy activated by ecdysone at the onset of Drosophila metamorphosis. We show here that E74A protein binds to three adjacent sites in the middle of the E74 gene. The consensus sequence for E74A protein binding, determined by random-sequence oligonucleotide selection, contains an invariant purine-rich core sequence, C/AGGAA. This sequence is also present in the binding sites of two mammalian proteins that, like E74A, are related to the ets oncoprotein. Antibody staining of larval salivary gland polytene chromosomes revealed that E74A protein binds to both early and late ecdysone-inducible puffs. This study supports Ashburner's proposal that the early puffs encode site-specific DNA binding proteins that directly interact with the early and late ecdysone-inducible puffs.