Many of the proteins that are critical for Drosophila phototransduction assemble into a signaling complex, signalplex, through association with the PDZ-domain protein INAD. Some of these proteins depend on INAD for proper subcellular localization to the phototransducing organelle, the rhabdomere, making it difficult to assess any physiological function of this signaling complex independent of localization. Here we demonstrated that INAD bound directly to the NINAC myosin III, yet the subcellular localization of NINAC was normal in inaD mutants. Nevertheless, the INAD binding site was sufficient to target a heterologous protein to the rhabdomeres. Disruption of the NINAC/INAD interaction delayed termination of the photoreceptor response. Thus one role of this signaling complex is in rapid deactivation of the photoresponse.
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