A second opsin gene expressed in the ultraviolet-sensitive R7 photoreceptor cells of Drosophila melanogaster

We have identified a second Drosophila opsin gene, Rh4, which is expressed specifically in the ultraviolet-sensitive R7 photoreceptor cells. The two R7 opsins, Rh3 and Rh4, are expressed in nonoverlapping subsets of R7 cells. The Rh4 opsin shares 72% amino acid identity with Rh3, but is only about 35% homologous with the other 2 Drosophila opsins, ninaE and Rh2. Twenty-eight amino acids are conserved among all 4 invertebrate and 5 vertebrate opsin genes thus far sequenced, suggesting that these residues play an important role in rhodopsin function.