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Xanthine dehydrogenase expression in Neurospora crassa does not require a functional nit-2 regulatory gene
1Department of Biology, University of Virginia, Charlottesville 22901.
Biochemical Genetics
|February 1, 1988
Summary
Xanthine dehydrogenase (XDH) is synthesized even without the nit-2 gene, challenging its role as an essential regulator. This finding questions the nit-2 gene's general necessity in nitrogen metabolite repression.
Area of Science:
- Biochemistry
- Molecular Biology
- Mycology
Background:
- Xanthine dehydrogenase (XDH) initiates purine catabolism in N. crassa.
- XDH synthesis is regulated by glutamine repression and uric acid induction.
- The nit-2 gene is presumed to regulate secondary nitrogen metabolism pathways.
Purpose of the Study:
- To investigate the role of the nit-2 gene in regulating Xanthine dehydrogenase (XDH) synthesis and activity.
- To determine if nit-2 is an essential regulator in nitrogen metabolite repression.
Main Methods:
- Immunoblot analyses to detect XDH protein.
- Enzyme assays to measure XDH activity.
- Growth studies of mutant strains (nit-2, xdh-1, nit-1, -7, -8, -9) on different nitrogen sources.
Main Results:
- XDH protein and activity are present in nit-2 mutants.
- XDH expression in nit-2 mutants is still subject to nitrogen metabolite repression.
- Mutants lacking XDH activity or molybdenum cofactor grow on xanthine but not hypoxanthine.
Conclusions:
- The nit-2 gene is not essential for XDH synthesis or activity.
- The role of nit-2 as an obligate control element in nitrogen metabolite repression is questioned.
- XDH pathway mutants exhibit specific substrate utilization defects.