ISOLATION AND EXPRESSION OF AN ARRESTIN CDNA FROM THE HORSESHOE-CRAB LATERAL EYE

Electrophysiological studies of photoreceptors from the horseshoe crab Limulus polyphemus continue to provide fundamental new knowledge of t he photoresponse in invertebrates. Therefore, it is of particular inte rest to characterize the molecular components of the photoresponse in this system. Here we describe an arrestin cloned from a cDNA library c onstructed using poly(A)(+) RNA isolated from Limulus lateral eyes. Th e protein, deduced from the arrestin cDNA, is most similar to arrestin from locust antennae (56% identity) and Drosophila phosrestin I (53% identity). Limulus arrestin was expressed in a heterologous system, an d its properties were compared with those of a 46-kDa light-regulated phosphoprotein (pp46A) in Limulus photoreceptors described in previous studies from this laboratory. Arrestin and pp46A (a) have the same ap parent molecular weight on sodium dodecyl sulfate-polyacrylamide gel e lectrophoresis, (b) have an isoelectric point in the basic pH range, ( c) require calmodulin and elevated Ca2+ levels for phosphorylation, (d ) are immunoreactive with monoclonal antibody C10C10 directed against a sequence in bovine arrestin (S-antigen) that is perfectly conserved in the deduced arrestin protein, and (e) are associated with photorece ptors. We conclude that the arrestin described here and pp46A are the same protein. The results of this and previous studies show that in Li mulus photoreceptors, light regulates the phosphorylation of arrestin in complex ways.