A NOVEL PROTEIN ENCODED BY THE INAD GENE REGULATES RECOVERY OF VISUALTRANSDUCTION IN DROSOPHILA

lnaD(p215) is a point mutation that affects photoreceptor function in Drosophila. To understand the molecular basis of the defect, we isolat ed the InaD gene and found it encodes a photoreceptor-specific polypep tide of 674 residues. Within its sequence are two repeats that share r emarkable homology with a family of cytoskeleton-associated proteins t hat are involved in signal transduction. Patch-clamp recordings from i solated photoreceptor cells of InaD(p215) show a slow deactivation of the light-induced current. Th is defective deactivation of InaD appear s dependent on calcium influx; removal of extracellular calcium masks its abnormal phenotype. Moreover, InaD photoreceptors show increased s ensitivity to dim light. We propose that InaD is involved in the negat ive feedback regulation of the light-activated signaling cascade in Dr osophila photoreceptors.