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Two Drosophila melanogaster mutations block successive steps of de novo purine synthesis
Abstract:
Drosophila melanogaster purine auxotrophs ade2(1) and ade3(1) have been characterized biochemically. The ade2(1) strain is deficient in the fourth step of the de novo purine synthetic pathway catalyzed by phosphoribosylglycinamidine synthase (phosphoribosylformylglycinamide amidotransferase). The ade3(1) strain is deficient in the previous step catalyzed by phosphoribosylglycinamide formyltransferase (GART). The mutation responsible for the slightly leaky ade3(1) phenotype was characterized further. First, the mutant GART polypeptide was found to be of normal size and present at normal levels. Second, the GART-encoding region of the mutant was cloned, inserted into a yeast-Escherichia coli shuttle vector, and used to transform mutant yeast. Transformants showed very slight in vivo activity when compared to wild type, verifying that the mutation is in the GART coding sequence. Lastly, the region of the gene encoding GART activity from mutant and inbred parental strain flies was completely sequenced. A single base transition was found, leading to the substitution of a serine for a highly conserved glycine. These two mutations provide examples of blocks in the de novo purine synthetic pathway in a whole animal.
Insights
Biochemical characterization of Drosophila melanogaster purine auxotrophs revealed specific enzyme deficiencies in the de novo purine synthesis pathway. These findings offer insights into purine metabolism in a whole animal model.
Area of Science:
- Biochemistry
- Genetics
- Molecular Biology
Background:
- Purine biosynthesis is essential for cellular function.
- Understanding purine auxotrophs aids in metabolic pathway elucidation.
- Drosophila melanogaster serves as a model organism for genetic studies.
Purpose of the Study:
- To biochemically characterize two Drosophila melanogaster purine auxotrophs, ade2(1) and ade3(1).
- To identify the specific enzymatic defects in the de novo purine synthetic pathway.
- To elucidate the molecular basis of the ade3(1) mutation.
Main Methods:
- Biochemical assays to determine enzyme activity.
- Genetic complementation using yeast-Escherichia coli shuttle vectors.
- DNA sequencing of the GART gene.
Main Results:
- The ade2(1) strain is deficient in phosphoribosylglycinamidine synthase.
- The ade3(1) strain has a defect in phosphoribosylglycinamidine formyltransferase (GART).
- A single base transition in the GART gene of ade3(1) results in a serine substitution for a conserved glycine, causing a leaky phenotype.
Conclusions:
- These mutations represent functional blocks in the de novo purine synthetic pathway in Drosophila.
- The characterization provides valuable genetic and biochemical tools for studying purine metabolism.
- The study highlights the utility of Drosophila as a model for investigating fundamental metabolic pathways.