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Pyrimidine biosynthesis in Aspergillus nidulans. Isolation and characterisation of mutants resistant to
Abstract:
Mutants resistant to 5-fluorouracil, 5-fluorouridine and 5-fluorodeoxyuridine have been selected in Aspergillus nidulans. Growth tests combined with genetic analysis showed that mutations conferring resistance to fluoropyrimidines could occur in at least seven genes. Three of these fulE, fulF and furA were concerned with either the uptake of pyrimidines or their conversion to uridine monophosphate. The other four genes did not affect these functions. Mutations in fulA probably confer resistance by lowering ornithine transcarbamoylase, thereby making the normally arginine-specific carbamoyl phosphate pool available for increased uracil synthesis. Mutations in fulD may make the arginine-specific carbamoyl phosphate synthetase insensitive to inhibition or repression by arginine, and so lead to increased carbamoyl phosphate pool sizes, and increased uracil synthesis. Both fulA and fulD mutants suppress pyrA mutants which lack the uracil-specific carbamoyl phosphate synthetase. Mutations in fulB and fulC do not suppress pyrA, and so may act more directly to increase uracil synthesis. The synthesis of aspartate carbamoyl transferase in fulB7 strains is not repressed by uracil. fulC mutants are closely linked to the pyrA, B, C, N region which codes for the first two enzymes of pyrimidine biosynthesis, and may result in these enzymes being less sensitive to inhibition by uracil.
Insights
Researchers identified seven genes in Aspergillus nidulans conferring resistance to fluoropyrimidines like 5-fluorouracil. Some genes affect pyrimidine uptake or conversion, while others enhance uracil synthesis through novel mechanisms.
Area of Science:
- * Biochemistry and Molecular Biology
- * Genetics and Genomics
- * Mycology
Background:
- * Fluoropyrimidines, including 5-fluorouracil, are widely used in chemotherapy.
- * Understanding resistance mechanisms is crucial for improving therapeutic efficacy.
- * Aspergillus nidulans serves as a model organism for studying pyrimidine biosynthesis and drug resistance.
Purpose of the Study:
- * To identify and characterize genes conferring resistance to fluoropyrimidines in Aspergillus nidulans.
- * To elucidate the biochemical and genetic basis of fluoropyrimidine resistance.
- * To investigate the role of specific genes in pyrimidine metabolism and drug sensitivity.
Main Methods:
- * Selection and genetic analysis of fluoropyrimidine-resistant mutants in Aspergillus nidulans.
- * Growth tests to assess resistance phenotypes.
- * Enzyme assays and genetic complementation to determine gene functions.
Main Results:
- * Mutations conferring resistance to 5-fluorouracil, 5-fluorouridine, and 5-fluorodeoxyuridine were identified in at least seven distinct genes (fulA-G).
- * Three genes (fulE, fulF, furA) are involved in pyrimidine uptake or conversion to uridine monophosphate.
- * Four genes (fulA, fulB, fulC, fulD) affect pyrimidine biosynthesis pathways, leading to increased uracil synthesis through various mechanisms, including altered enzyme activity and feedback regulation.
Conclusions:
- * Fluoropyrimidine resistance in Aspergillus nidulans is genetically complex, involving multiple genes.
- * Resistance can arise from alterations in pyrimidine transport, metabolism, or de novo synthesis pathways.
- * The identified genes provide insights into the regulation of pyrimidine biosynthesis and potential targets for overcoming drug resistance.