Molecular defects in Drosophila rhodopsin mutants.

Four well characterized Drosophila rhodopsin (ninaE) mutants possess low levels of rhodopsin in their major class of photoreceptors. The molecular defect present in each strain was determined by isolating and sequencing the mutant genes. Two missense mutants encode proteins which have arginine residues positioned within membrane-spanning domains. The third missense mutant eliminates a proline found near an extracellular domain/membrane-spanning domain interface. Thus, the low levels of rhodopsin protein found in these mutants result directly from changes in protein structure which likely affect the positioning and stability of membrane-spanning domains. The fourth and most severe mutation is a nonsense mutation.