Maturation of major Drosophila rhodopsin, ninaE, requires chromophore 3-hydroxyretinal.

Opsin expression is extremely suppressed by carotenoid deprivation in Drosophila. Carotenoid replacement in deprived flies promotes the recovery of visual pigment with an increase in opsin, as well as the chromophore 11-cis-3-hydroxyretinal. Here, we show that opsin mRNA and opsin peptide in an intermediate step of posttranslational processing were present in carotenoid-deprived flies. By supplementing chromophore to photoreceptor cells, intermediate opsin was made mature. During this process, opsin peptide underwent multiple modifications involving glycosylation. Based on these results, we present a novel mechanism of protein regulatory expression; that is, chromophore posttranslationally controls the expression of apoprotein by promoting its maturation.