OPSINS FROM THE LATERAL EYES AND OCELLI OF THE HORSESHOE-CRAB, LIMULUS-POLYPHEMUS

cDNA clones encoding opsins from the lateral eyes and median ocelli of the horseshoe crab, Limulus polyphemus, were isolated from cDNA libra ries. The opsin cDNAs obtained from the lateral eye and ocellar librar ies code for deduced proteins with 376 amino acids. The two cDNAs are 96% identical at the nucleic acid level, differing primarily at the 3' untranslated region, and are apparently the products of two separate genes. The deduced opsin proteins are 99% identical to each other, dif fering at only 5 amino acids. The opsins encoded by these cDNAs are mo st likely the protein moiety of the visible-wavelength rhodopsins in t his animal. In the lateral eye, expression of the opsin gene is restri cted to the photoreceptor cells of the ommatidia. Comparisons with ops ins of other species show that the Limulus opsin proteins are most sim ilar (53% identity) to the opsin from the R1-6 photoreceptors of flies .