IDENTIFICATION AND CHARACTERIZATION OF A DROSOPHILA NUCLEAR RECEPTOR WITH THE ABILITY TO INHIBIT THE ECDYSONE RESPONSE

In a search for retinoid X receptor-like molecules in Drosophila, we h ave identified an additional member of the nuclear receptor superfamil y, XR78E/F. In the DNA-binding domain, XR78E/F is closely related to t he mammalian receptor TR2, as well as to the nuclear receptors Coup-TF and Seven-up. We demonstrate that XR78E/F binds as a homodimer to dir ect repeats of the sequence AGGTCA. In transient transfection assays, XR78E/F represses ecdysone signaling in a DNA-binding-dependent fashio n. XR78E/F has its highest expression in third-instar larvae and prepu pae. These experiments suggest that XR78E/F may play a regulatory role in the transcriptional cascade triggered by the hormone ecdysone in D rosophila.