CONE ARRESTIN IDENTIFIED BY TARGETING EXPRESSION OF A FUNCTIONAL FAMILY

High acuity, color vision in humans is initiated in cones by a recepto r/G-protein-linked phototransduction cascade. G-protein-linked recepto rs are rapidly deactivated by receptor phosphorylation and the binding of a member of the ''arrestin'' family of proteins. Divergence in ami no acid sequence at the carboxyl terminus of S-antigen (rod photorecep tor arrestin) and beta-arrestin 1 and beta-arrestin 2 (beta-adrenergic receptors) suggests that receptor specificity may be coded within thi s region. An anchor primer strategy was utilized to screen for carboxy l-terminal variability with a rat pineal library, identifying three kn own arrestins plus three unknowns (C-arrestin, D-arrestin, and E-arres tin). cDNA was prepared by reverse transcription of mRNA from 12 rat t issues, and members of the arrestin family were amplified by polymeras e chain reaction using the anchor primer and customized 3'-primers for the individual arrestins. The amplified arrestins were then digested by selected restriction endonucleases, producing a pattern of characte ristic cleavage products for each arrestin isoform. The procedural com bination of epitope domain anchor and tissue screening demonstrated th at C-arrestin is enriched in the retina. C-arrestin was isolated from a lambda MAX1 human retinal cDNA library and sequenced, revealing sign ificant identity to known arrestins and divergence within the 3'-regio n. The mRNA for C-arrestin was visualized by in situ hybridization, lo calizing in the retina with cone photoreceptors and in the pineal to a subpopulation of pinealocytes. A gene for human C-arrestin was mapped to the X chromosome, making C-arrestin a candidate for several inheri ted X-linked retinopathies. The localization of C-arrestin to cone pho toreceptors suggests that it, like others in the arrestin family, may bind to phosphorylated receptors and participate in deactivation of th e phototransduction cascade.