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The regulation of nitrate assimilation in Neurospora crassa: Biochemical analysis of the nmr-1 mutants

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Summary

Neurospora crassa nmr-1 mutants, selected on the basis of their sensitivity to chlorate in the presence of glutamine, have elevated levels of the nitrate assimilation enzymes, NADPH-nitrate reductase and NAD(P)H-nitrite reductase. Immunoelectrophoretic determinations show that the higher nitrate reductase activities in nmr-1 mutants are due to greater enzyme concentrations. The half-life of nitrate reductase in these mutants is unaltered. As in wild-type, expression of nitrate assimilation in nmr-1 mutants is dependent on induction by nitrate. Reduced nitrogen metabolites like ammonium and glutamine still repress this expression in nmr-1 mutants, but not as effectively as in wild-type. Enzymatic activity measurements in double mutant strains confirm that the nit regulatory loci, nit-2 and nit-4/5, are epistatic to nmr-1, but nmr-1 is epistatic to nit-3, the nitrate reductase structural gene. The results imply that nmr-1 is involved in post-transcriptional control of nitrate assimilation.

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Author notes

  1. A. Brian Tomsett

    Present address: Department of Genetics, University of Nottingham, NG7 2RD, Nottingham, England

Authors and Affiliations

  1. Department of Biology, University of Virginia, Gilmer Hall, 22901, Charlottesville, Virginia, USA

    Nigel S. Dunn-Coleman, A. Brian Tomsett & Reginald H. Garrett

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  1. Nigel S. Dunn-Coleman
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  2. A. Brian Tomsett
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  3. Reginald H. Garrett
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Communicated by W. Gajewski

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Dunn-Coleman, N.S., Tomsett, A.B. & Garrett, R.H. The regulation of nitrate assimilation in Neurospora crassa: Biochemical analysis of the nmr-1 mutants. Molec. Gen. Genet. 182, 234–239 (1981). https://doi.org/10.1007/BF00269663

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  • DOI: https://doi.org/10.1007/BF00269663

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