A novel, evolutionarily conserved enhancer of cone photoreceptor-specific expression.

The alpha subunit of cone transducin (TalphaC) is expressed exclusively in cone photoreceptors of the eye and pineal. TalphaCisakey phototransduction protein, and inherited mutations in TalphaC cause total color blindness in humans. We use transgenic zebrafish to identify and characterize cone photoreceptor regulatory element 1 (CPRE-1) a novel 20-bp enhancer element in the TalphaC promoter (TalphaCP). CPRE-1 is located approximately 2.5 kb upstream of the translation start site and is necessary for strong cone photoreceptor-specific expression in vivo. CPRE-1 comprises of a modular arrangement of two 10-bp elements that have separate, but co-dependent transcriptional activities. In vitro, CPRE-1 specifically binds nuclear factors that are enriched in ocular tissue. Bioinformatic alignments reveal that CPRE-1 sites are evolutionarily conserved in the promoter regions of fish, rodent, and mammalian TalphaC orthologues and identify a 5'-CTGGAGTG(A/T)TGGA(G/A)GCAGGG(G/C)T-3' consensus sequence.