Characterization and partial purification of the Drosophila Kc cell ecdysteroid receptor

The molting hormones of insects, the ecdysteroids, are steroids whose action is mediated by an intracellular receptor. The Kc cell line of Drosophila melanogaster possesses ecdysteroid receptors and exhibits characteristic, receptor-dependent morphological and biochemical responses to the application of ecdysteroids. This paper describes the interaction of muristerone A (2 beta, 3 beta, 5 beta, 11 alpha, 14 alpha(20R,22R)- heptahydroxycholest-7-en-6-one), a phytoecdysteroid, with the Kc cell ecdysteroid receptor. Muristerone A-receptor complexes are not as sensitive to dissociation in high salt buffers as other ecdysteroid-receptor complexes we have examined. This has enabled us to use [3H]muristerone A to follow the Kc cell ecdysteroid receptor during heparin-agarose, DNA-cellulose, and hydroxylapatite chromatography, as well as gel filtration and ion exchange high pressure liquid chromatography. The Drosophila Kc cell ecdysteroid receptor has a Stokes radius of 4.6 nm, a frictional coefficient of 1.4, and a molecular weight of 120,000. A procedure is presented that results in a 750-fold enrichment of the receptor.