A Visual Pigment from Chicken that Resembles Rhodopsin: Amino Acid Sequence, Gene Structure, and Functional Expression

The amino acid sequence of a rhodopsin-like visual pigment from chickens has been determined by isolating and sequencing its gene. The predicted sequence is between 70% and 80% identical to bovine, human, and chicken rhodopsins and between 40% and 50% identical to human blue, green, and red cone pigments, the chicken red cone pigment, and cavefish long-wave cone pigments. The encoded pigment, produced by transfection of cDNA into cultured cells, absorbs maximally at 495 nm as determined from photobleaching difference spectra and reacts at 20 °C with 50 mM hydroxylamine with a half-time of 16 min. These properties, together with a high pI predicted from the amino acid sequence, suggest that this cloned gene encodes the chicken green pigment previously identified by biochemical and spectroscopic studies. This sequence defines a new branch of the visual pigment gene family.