A genetic and molecular characterization of the garnet gene of Drosophila melanogaster

The garnet gene was one of the first genes to be identified in Drosophila m elanogaster. Mutations in the garnet gene affect both of the biochemically distinct types of pigments in the eye and disrupt pigmentation of other org ans. As an initial step in the analysis of this gene, we have analyzed the pigmentation defects in several of the garnet alleles. We have also cloned the gene and examined its expression in various tissues and at different st ages of development. The garnet gene is expressed throughout development an d in all tissues examined. Structurally related sequences can be detected i n a variety of other eukaryotes. The predicted protein sequence of the garn et product resembles clathrin and nonclathrin adaptin proteins and is highl y similar to the delta subunit of the newly isolated mammalian AP-3 adaptin complex, which is associated with the trans-Golgi network and endosomes. T his suggests that garnet encodes a protein that acts in the intracellular s orting and trafficking of vesicles from the trans-Golgi network to endosome s, and related specialized organelles such as the pigment granule. This fin ding provides an explanation for the phenotype of garnet mutations and pred icts that other Drosophila eye-colour genes will be a rich resource for the genetic dissection of intracellular vesicle transport.