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

The alpha subunit of cone transducin (T alpha C) is expressed exclusively in cone photoreceptors of the eye and pineal. T alpha C is a key phototransduction protein, and inherited mutations in T alpha C 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 T alpha C promoter (T alpha CP). CPRE-1 is located similar to 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 T alpha C orthologues and identify a 5'-CTGGAGTG(A/T) TGGA(G/A) GCAGGG(G/C) T-3' consensus sequence.