The cyclophilin homolog ninaA is a tissue-specific integral membrane protein required for the proper synthesis of a subset of Drosophila rhodopsins.

Mutations in the Drosophila ninaA gene cause dramatic reductions in rhodopsin levels, leading to impaired visual function. The ninaA protein is a homolog of peptidyl-prolyl cis-trans isomerases. We find that ninaA is unique among this family of proteins in that it is an integral membrane protein, and it is expressed in a cell type-specific manner. We have used transgenic animals misexpressing different rhodopsins in the major class of photoreceptor cells to demonstrate that ninaA is required for normal function by two homologous rhodopsins, but not by a less conserved member of the Drosophila rhodopsin gene family. This demonstrates in vivo substrate specificity in a cyclophilin-like molecule. We also show that vertebrate retina contains a ninaA-related protein and that ninaA is a member of a gene family in Drosophila. These data offer insights into the in vivo role of this important family of proteins.