The ninaA gene required for visual transduction in Drosophila encodes a homologue of cyclosporin A-binding protein

Abstract

MUTATIONS of the Drosophila melanogaster ninaA gene affect phototransduction: ninaA mutant flies have a 10-fold reduction in the levels of rhodopsin in the R1–R6 photoreceptor cells^1,2. The ninaA gene was isolated and found to encode a 237-amino-acid protein that has over 40% amino-acid sequence identity with the vertebrate cyclosporin A-binding protein, cyclophilin, a protein that seems to be involved in T-lymphocyte activation. The remarkable evolutionary conservation of cyclophilin in two phylogeneti-cally distant organisms and its involvement in diverse transduction processes suggests that this protein plays an important role in cellular metabolism. Indeed, cyclophilin has recently been shown to be a prolyl cis–trans isomerase that catalyses, in vitro, rate-limiting steps in the folding of a number of proteins^3,23. Here, we present evidence for the involvement of cyclophilin-like molecules in a defined cellular process. The availability of mutations in a cyclophilin gene provides a new model system for the study of cyclophilin and cyclosporin action.