A novel protein encoded by the InaD gene regulates recovery of visual transduction in Drosophila.

InaDp215 is a point mutation that affects photoreceptor function in Drosophila. To understand the molecular basis of the defect, we isolated the InaD gene and found it encodes a photoreceptor-specific polypeptide of 674 residues. Within its sequence are two repeats that share remarkable homology with a family of cytoskeleton-associated proteins that are involved in signal transduction. Patch-clamp recordings from isolated photoreceptor cells of InaDp215 show a slow deactivation of the light-induced current. This defective deactivation of InaD appears dependent on calcium influx; removal of extracellular calcium masks its abnormal phenotype. Moreover, InaD photoreceptors show increases sensitivity to dim light. We propose that InaD is involved in the negative feedback regulation of the light-activated signaling cascade in Drosophila photoreceptors.