BOVINE PHOSPHOLIPASE-C HIGHLY HOMOLOGOUS TO THE NORPA PROTEIN OF DROSOPHILA IS EXPRESSED SPECIFICALLY IN CONES

The Drosophila norpA gene encodes a phosphatidylinositol-specific phos pholipase C (PI-PLC) expressed predominantly in photoreceptors and inv olved in phototransduction. However, no direct role for a phospholipas e C in vertebrate phototransduction has been identified to date. Recen tly, we reported the isolation and characterization of bovine cDNAs en coding PI-PLC isoforms expressed predominantly in the retina and with higher homology to the NorpA protein than to any other known PI-PLC. H ere, we present evidence that the norpA-homologous bovine retinal PI-P LCs, although found in other retinal neurons as well, are found in con es but not in rods. The results suggest that the phototransduction cas cade in cones may utilize phospholipase C in addition to phosphodieste rase.