IN-SITU ASSAY OF LIGHT-STIMULATED G-PROTEIN ACTIVITY IN DROSOPHILA PHOTORECEPTOR G-PROTEIN BETA-MUTANTS

An in situ S-35-labeled guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) binding procedure was developed to assay light-stimulated G protei n activity in Drosophila compound eyes. We found that Drosophila with mutations in G beta e, an abundant photoreceptor-specific G protein be ta subunit essential for photoexcitation, are defective in light-stimu lated [S-35]GTP gamma S binding. We confirmed that G beta e interacts with a GTP-binding protein by demonstrating that immunoprecipitation o f G beta e is sensitive to GTP gamma S. These results suggest that G b eta e functions as the beta subunit of a heterotrimeric G protein that couples photoactivation of rhodopsin to down-stream components in the Drosophila phototransduction cascade.