Nitrogen metabolite repression of nitrate reductase in Neurospora crassa

Abstract

The effect of different nitrogen compounds on the induction of reduced nicotinamide adenine dinucleotide phosphate-nitrate reductase was examined in Neurospora crassa. Whereas in the wild-type strain several amino acids and ammonia inhibit the formation of nitrate reductase, only glutamine, cysteine, and histidine are shown to inhibit the synthesis of nitrate reductase in a glutamine-requiring auxotroph. None of the amino acids inhibited nitrate reductase activity in vitro. The effects of cysteine and histidine are nonspecific, these amino acids being inhibitory to the growth of the organism. The effect of glutamine on the induction of nitrate reductase is not due to an inhibition of the uptake of the inducer nitrate. By the use of histidine-, pyrimidine-, and arginine-requiring auxotrophs, it was shown that glutamine appears to act per se and does not seem to be converted to another product in order to be effective in repression. The repression of nitrate reductase by ammonia appears, from the results described herein, to be indirect; ammonia has to be converted first to glutamine in order to be effective in repression.

Regulation of nitrate reductase levels in the cyanobacteria Anacystis nidulans, Anabaena sp. strain 7119, and Nostoc sp. strain 6719

“…From experiments with wild-type and mutant strains of the fungus Neurospora crassa, a decisive role of glutamine synthetase in the "ammonium repression" effect on nitrate reductase synthesis has also been reported recently (4,15). It has been proposed that either glutamine or some particular derivative of glutamine is the actual repressor (15) or that glutamine synthetase itself is the putative regulator in nitrogen metabolite repression (4). Although our results do not allow a decision about the nature of the true repressor, they clearly show that inactivation of glutamine synthetase resulted in the disappearance of the repressive effect of ammonium.…”

“…Our results from experiments with MSX and A. nidulans strongly suggest that ammonium per se is not the true repressor, but that it has to be metabolized through glutamine synthetase before a repressive effect on nitrate reductase is manifested. From experiments with wild-type and mutant strains of the fungus Neurospora crassa, a decisive role of glutamine synthetase in the "ammonium repression" effect on nitrate reductase synthesis has also been reported recently (4,15). It has been proposed that either glutamine or some particular derivative of glutamine is the actual repressor (15) or that glutamine synthetase itself is the putative regulator in nitrogen metabolite repression (4).…”

and , two new involved in nitrogen metabolite repression

“…Indeed, glutamine and/or glutamate are thought the be crucial molecules for signalling the nitrogen nutritional status; in addition, Are À mutants, impaired on GS activity or NADPH-GDH activity, have been described in A. nidulans and in N. crassa. While showing a leaky weak growth on ammonium plates, these mutants exhibit wild-type phenotype on media containing glutamine or glutamate as nitrogen source [78][79][80][81][82][83][84][85][86]. In order to test this possibility we analysed the GS and the NADPH-GDH activities of our mutants on different nitrogen sources.…”

Regulation of induction of nitrate reductase and nitrite reductase in higher plants

“…These results indicate that the major effect of NOj is due to the induction of new NR and NIR molecules via gene expression. However, earlier studies with fungi have indicated that NOJ was not essential for transcription of NR genes and that the effect of NOj is to etihance accumulation of the transcripts (Garret and Amy 1978, Premakumar et al, 1979), Recent studies have further indicated that NOJ supply might also effect mRNA stability (Yamazaki et al, 1986). Thus the question becomes obvious whether NOj-induced appearance of NR transacts is only due to the synthesis of fresh mRNA, or whether NOj affects stability of the already existing transcripts as well,…”