The phototransduction cascade in vertebrate rod and cone photoreceptors is initiated by a light-induced conformational change in the visual pigment rhodopsin. The visual pigments are members of the seven-transmembrane domain, G-protein coupled receptor superfamily and consist of an apoprotein, opsin, and a chromophore, 11-cis-retinal. Rods and each cone type express a different opsin gene. The peak wavelength of light absorption by the 11-cis-retinal in each opsin is determined by the chromophore environment created by the surrounding amino acid sidechains. The developmental expression of opsin is under transcriptional control and begins soon after the rod cells become postmitotic (Treisman et al., 1988). We, and others, have analyzed the cis and trans-acting factors that regulate opsin transcription and have suggested that a single element, RET 1, is critical for both temporal and spatial regulation of opsin expression (Morabito et al., 1991; Yu et al., 1993). We used a subclone of a bovine opsin cDNA to screen an EcoRI rat genomic Charon 4A library (Clontech, Palo Alto, CA) under stringent hybridization conditions. A 6.8-kb clone was found to contain approx 2 kb of 5' sequence, the entire coding sequence, and much of the 3' untranslated sequence. The 5' sequence has been analyzed in detail and has been described elsewhere (Morabito et al., 1991; Yu et al., 1993; GenBank accession number L01537).