Cloning and molecular characterization of a metabolic gene with development functions in Drosophila. I. Analysis of the head function of Punch.

In an effort to understand the functions of pterins throughout development we have been studying Punch (Pu), the structural gene for the enzyme GTP cyclohydrolase in Drosophila melanogaster. This enzyme catalyzes the first step in the pterin biosynthetic pathway. The Pu gene product is required for vital functions at two distinct stages in embryogenesis, and a pigmentation function in the eye of the young adult. We have localized the Pu region to 29 kb of DNA through the analysis of lesions present in Pu mutants. Since all of the mutations that were mapped affect the eye pigmentation function of Pu, and since this function is the best defined biochemically, we have concentrated on identifying and characterizing Pu products required for eye pigmentation in our initial examination of the cloned region. Four different transcripts from this region are expressed in the adult head. We show that one of these transcripts, the 1.7-kb species, is responsible for the pigmentation function through the analysis of mutant transcripts and the use of an in vitro translation assay. A 2-kb region lying within the locus is specifically required for this eye pigmentation function.