PINEAL OPSIN - A NONVISUAL OPSIN EXPRESSED IN CHICK PINEAL

Pineal opsin (P-opsin), an opsin from chick that is highly expressed i n pineal but is not detectable in retina, was cloned by the polymerase chain reaction. It is likely that the P-opsin lineage diverged from t he retinal opsins early in opsin evolution. The amino acid sequence of P-opsin is 42 to 46 percent identical to that of the retinal opsins. P-opsin is a seven-membrane spanning, G protein-linked receptor with a Schiff-base lysine in the seventh membrane span and a Schiff-base cou nterion in the third membrane span. The primary sequence of P-opsin su ggests that it will be maximally sensitive to similar to 500-nanometer tight and produce a slow and prolonged phototransduction response con sistent with the nonvisual function of pineal photoreception.