Demonstration of an Ecdysteroid Receptor in a Cultured Cell Line of Drosophila melanogaster

Incubation of the high-speed supernatant from the Kc cell line of Drosophila melanogaster with [3H]ponasterone A results in significant binding of the ligand as determined by gel filtration and dextran-coated charcoal binding assays. In vivo exposure of the Kc line to [3H]ponasterone A for 30 min results in a marked binding of the ligand by a KCl-soluble nuclear extract. With both the cytosol and nuclear preparations the binding has specificity and a low dissociation constant (3 × 10-9 M). In addition the labeling of the nuclear preparation exhibits a saturation at approximately 7 × 10-10 M which probably reflects the molar concentration of cytoplasmic receptors.