Bovine phospholipase C highly homologous to the norpA protein of Drosophila is expressed specifically in cones.

The Drosophila norpA gene encodes a phosphatidylinositol-specific phospholipase C (PI-PLC) expressed predominantly in photoreceptors and involved in phototransduction. However, no direct role for a phospholipase C in vertebrate phototransduction has been identified to date. Recently, we reported the isolation and characterization of bovine cDNAs encoding PI-PLC isoforms expressed predominantly in the retina and with higher homology to the NorpA protein than to any other known PI-PLC. Here, we present evidence that the norpA-homologous bovine retinal PI-PLCs, although found in other retinal neurons as well, are found in cones but not in rods. The results suggest that the phototransduction cascade in cones may utilize phospholipase C in addition to phosphodiesterase.