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 domi nant resistance to alpha-methyl dopa and suggest the gene is involved in ca techolamine metabolism. Evidence for involvement in catecholamine metabolis m comes from the three phenotypes associated with the mutant Tcr chromosome s - dominant resistance, dominant rescue of partially complementing l(2)amd alleles, and recessive lethal phenotypes. Only dominant resistance to alph a s-methyl dopa, however, was mapped to the Tcr locus. Both recessive letha lity 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 demons trate these phenotypes are due to a loss of Tcr function. This deletion pla ces the Tcr gene in the 69B4-5 to 69C8-11 region. Additionally, we have tes ted and verified three predictions of the biochemical model proposed by Bis hop, Sherald, and Wright (1989) for the function of the Tcr protein.