Rudimentary mutants ofDrosophila melanogaster
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The X-linkedrudimentary (r) mutants ofDrosophila melanogaster are pyrimidine auxotrophs and require exogenous pyrimidines (Nørby, 1970; Falk, 1976). We have established a set ofrudimentary cell lines that are derived from embryos, homozygous for eitherr1 orr36. The enzymatic activities of the pyrimidine synthesizing enzymes were measured in the mutant lines. We have further investigated the nutritional requirements of the mutant cells in vitro by using a pyrimidine free culture medium.
Ther1 cell lines were found to express 3–7%dihydroorotase (DHOase) activity as compared to a wildtype cell line. Reducedaspartate transcarbamylase (ATCase) activity was measured in somer1 cell lines whereas wildtypecarbamylphosphate synthetase (CPSase) activity is expressed in allr1 cell lines. Ther36 cell line expresses wildtype activity ofDHOase andCPSase. ATCase activity was found to be reduced to 10% of the wildtype activity.
The mutant cell lines do not proliferate in pyrimidine free minimal medium and cell proliferation is obtained by the addition of crude RNA. Proliferation of ther1 cells is restored by the supplementation of the minimal medium withdihydroorotate whereas proliferation of ther36 cells is restored by supplementation with eitherdihydroorotate orcarbamylaspartate.
The results demonstrate that therudimentary phenotypesr1 andr36 are expressed at the cellular level and that the two mutant cell types behave as cellular pyrimidine auxotrophs in vitro.
Key wordsPyrimidine biosynthesis rudimentary mutants Drosophila melanogaster
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