Increased Expression of Chloramphenicol Acetyltransferase by Carotenoid and Retinoid Replacement in Drosophila Opsin Promoter Fusion Stocks

Drosophila promoter fusion stocks containing a chloramphenicol acetyltransferase (CAT) reporter gene fused to a 2·8 kb DNA fragment from the Rh1 opsin promoter were carotenoid deprived from egg to adult, and then adults were replaced by feeding carrot juice. CAT activity, determined by radiometric assay, was low in deprived flies; it increased rapidly during the first 3 days of replacement and then declined back to the control level. Retinoic acid increased peak CAT activity as much as carrot juice and more than β-carotene, all- trans retinol or all- trans retinal. These findings suggest that vitamin A serves not only as rhodopsin's chromophore but also influences Rh1 opsin gene transcription. Three stocks with various deletions in the Rh1 opsin promoter lacked the carrot juice-dependent elevation of CAT activity. All three deletions include the region from -701 to -488, suggesting that this region may contain a vitamin A-responsive DNA sequence.