The biochemical genetics of rudimentary mutants of Drosophila melanogaster. I. Aspartate carbamoyltransferase levels in complementing and non-complementing strains.

Aspartate carbamoyltransferase (ACT) levels were determined in larvae from two completely complementing and one non-complementing rudimentary strain, as well as in wild-type larvae. The levels were low in the non-complementing and in one of the complementing strains, whereas the other complementing strain had wild-type levels. When viewed together with the previous findings of a nutritional requirement for pyrimidines in the non-complementing strain, that can be satisfied by carbamoyl aspartate, these results indicate that the rudimentary locus determines the first two enzyme activities in the pyrimidine biosynthetic pathway; carbamoyl phosphate synthetase and aspartate carbamoyltransferase. Addition of uracil to the culture medium caused no decrease in the level of ACT in wild type or ACT-positive rudimentary larvae indicating that end product repression of this enzyme does not take place in Drosophila.