The "five-sites" rule and the evolution of red and green color vision in mammals

Amino acid changes S180A (S-->A at site 180), H197Y, Y277F, T285A, andA308S are known to shift the maximum wavelength of absorption (lambda max)of red and green visual pigments toward blue, essentially in an additivefashion. To test the generality of this "five-sites" rule, we havedetermined the partial amino acid sequences of red and green pigments fromfive mammalian orders (Artiodactyla, Carnivora, Lagomorpha, Perissodactyla,and Rodentia). The result suggests that cat (Felis catus), dog (Canisfamiliaris), and goat (Capra hircus) pigments all with AHYTA at the fivecritical sites have lambda max values of approximately 530 nm, whereas rat(Rattus norvegicus) pigment with AYYTS has a lambda max value ofapproximately 510 nm, which is accurately predicted by the five-sites rule.However, the observed lambda max values of the orthologous pigments ofEuropean rabbit (Oryctolagus cuniculus), white-tailed deer (Odocoileusvirginianus), gray squirrel (Sciurus carolinensis), and guinea pig (Caviaprocellus) are consistently more than 10 nm higher than the predictedvalues, suggesting the existence of additional molecular mechanisms for redand green color vision. The inferred amino acid sequences of ancestralorganisms suggest that the extant mammalian red and green pigments appearto have evolved from a single ancestral green-red hybrid pigment bydirected amino acid substitutions.