Cytological location and further characterization of the Third chromosome resistance gene in Drosophila melanogaster.

Mutations in the Third chromosome resistance (Tcr; 3-39.6) gene confer dominant resistance to alpha-methyl dopa and suggest the gene is involved in catecholamine metabolism. Evidence for involvement in catecholamine metabolism comes from the three phenotypes associated with the mutant Tcr chromosomes--dominant resistance, dominant rescue of partially complementing l(2)amd alleles, and recessive lethal phenotypes. Only dominant resistance to alpha s-methyl dopa, however, was mapped to the Tcr locus. Both recessive lethality and dominant rescue of l(2)amd alleles have now been mapped to the Tcr gene and, through the isolation of a new deletion in the region, we demonstrate these phenotypes are due to a loss of Tcr function. This deletion places the Tcr gene in the 69B4-5 to 69C8-11 region. Additionally, we have tested and verified three predictions of the biochemical model proposed by Bishop, Sherald, and Wright (1989) for the function of the Tcr protein.