Cone arrestin identified by targeting expression of a functional family

High acuity, color vision in humans is initiated in cones by a receptor/G-protein-linked phototransduction cascade. G-protein-linked receptors are rapidly deactivated by receptor phosphorylation and the binding of a member of the "arrestin" family of proteins. Divergence in amino acid sequence at the carboxyl terminus of S-antigen (rod photoreceptor arrestin) and beta-arrestin 1 and beta-arrestin 2 (beta-adrenergic receptors) suggests that receptor specificity may be coded within this region. An anchor primer strategy was utilized to screen for carboxyl-terminal variability with a rat pineal library, identifying three known arrestins plus three unknowns (C-arrestin, D-arrestin, and E-arrestin). cDNA was prepared by reverse transcription of mRNA from 12 rat tissues, and members of the arrestin family were amplified by polymerase 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 characteristic cleavage products for each arrestin isoform. The procedural combination of epitope domain anchor and tissue screening demonstrated that C-arrestin is enriched in the retina. C-arrestin was isolated from a lambda MAX1 human retinal cDNA library and sequenced, revealing significant identity to known arrestins and divergence within the 3'-region. The mRNA for C-arrestin was visualized by in situ hybridization, localizing 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 inherited X-linked retinopathies. The localization of C-arrestin to cone photoreceptors suggests that it, like others in the arrestin family, may bind to phosphorylated receptors and participate in deactivation of the phototransduction cascade.