Ectopic expression of a minor Drosophila opsin in the major photoreceptor cell class: distinguishing the role of primary receptor and cellular context.

We have used P-element-mediated transformation to introduce the cloned Rh1 rhodopsin gene into the germ line of Drosophila and fully rescue the visual phenotype of mutant ninaE flies. A transcriptional fusion between the ninaE promoter and the structural gene for a minor opsin (Rh2) that is not normally expressed in the R1-R6 photoreceptor cells was used to demonstrate that Rh2 rhodopsin can photoactivate the R1-R6 transduction cascade, but with different spectral sensitivity. In addition, we show that two mutants that specifically affect the R1-R6 cells, ninaA and rdgB, do not directly affect expression of the ninaE gene.