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

✍ Scribed by Dunn-Coleman, Nigel S. ;Tomsett, A. Brian ;Garrett, Reginald H.

• Publisher: Springer
• Year: 1981
• Tongue: English
• Weight: 567 KB
• Volume: 182
• Category: Article
• ISSN: 0026-8925
• DOI: 10.1007/bf00269663

✦ Synopsis

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.