The SOCS box protein STOPS is required for phototransduction through its effects on phospholipase C

Phosphoinositide-specific phospholipase C (PLC) isozymes play roles in a diversity of processes including Drosophila phototransduction. In fly photoreceptor cells, the PLC P encoded by norpA is critical for activation of TRP channels. Here, we describe a PLC beta regulator, STOPS, which encodes a SOCS box protein. Mutation of stops resulted in a reduced concentration of NORPA and a defect in stopping signaling following cessation of the light stimulus. NORPA has been proposed to have dual roles as a PLC- and GTPase-activating protein (GAP). We found that the slow termination resulting from expressing low levels of wild-type NORPA was suppressed by addition of normal amounts of an altered NORPA, which had wild-type GAP activity, but no PLC activity. STOPS is the first protein identified that specifically regulates PLC beta protein concentration. Moreover, this work demonstrates that a PLC beta derivative that does not promote TRP channel activation, still contributes to signaling in vivo.