Zebrafish ultraviolet visual pigment: absorption spectrum, sequence, and localization

Abstract

In many vertebrates, UV-sensitive photoreceptors have been identified by microspectrophotometry and UV-visual sensitivity has been identified by behavioral studies, but as yet no vertebrate UV-sensitive pigment gene has been isolated. We have sequenced a cDNA clone that hybridizes to short single cone cells in the zebrafish (Brachydanio rerio). These cells, which make up 25% of the cone population in zebrafish retinae, are UV-sensitive (lambda max approximately 360 nm). The visual pigment encoded by this gene is unusual in that its amino acid sequence is more homologous to the rod pigment rhodopsin (up to 89%) than to other cone pigments (35-83%). Like all other vertebrate visual pigments, it contains a lysine residue at position 296, the presumptive retinal binding site, and a glutamate residue at position 113. However, it is unique in possessing a lysine residue at position 126, which may account for the UV-sensitivity of the pigment.