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We describe the identification of a novel opsin gene isolated from the eyes of Atlantic salmon. The cDNA sequence predicts a protein that has the key features of an opsin, but shows only 32-42% amino acid identity to the known opsin families. Phylogenetic analysis suggests that this opsin is a member of a hitherto unrecognised opsin family that diverged early in the evolution of vertebrate photopigments. We have tentatively called this opsin family the vertebrate ancient (VA) opsins. The identification of VA opsin may ultimately help to resolve some of the uncharacterised photoreceptor functions of the eye, which include the regulation of circadian rhythms, pupil size and corneal pigmentation.
Soni et al. (Mon,) studied this question.