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Query: EC:1.7.1.2 (nitrate reductase)
 3,861 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A transformation procedure based on the complementation of a genetic defect was developed using a nitrate reductase-deficient mutant of Aspergillus flavus. The initial transformation efficiency was improved 40-fold by combining factors in a planned experimental program. Although low, this transformation rate was sufficient to obtain transformants in which the urate oxidase-encoding gene (uaZ) was disrupted in a gene replacement experiment. These new uaZ- strains were unable to utilize uric acid as the unique nitrogen source and could be reversed directly to the wild-type phenotype in second order transformation experiments using a urate oxidase-expressing vector.
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PMID:Transformation of Aspergillus flavus: construction of urate oxidase-deficient mutants by gene disruption. 161 33

Neurospora crassa possesses a set of nitrogen-regulated enzymes whose expression requires a lifting of nitrogen catabolite repression and specific induction. The nit-2 gene is a major regulatory locus which appears to act in a positive way to turn on the expression of these nitrogen-related enzymes whereas the nit-4 gene appears to mediate nitrate induction of nitrate and nitrite reductase. The nit-3 gene specifies nitrate reductase and is subject to control by both nit-2 and nit-4. Many new nit-2, nit-3, and nit-4 mutants were isolated in order to obtain amber nonsense mutations in these loci which were suppressible by the suppressor gene, Ssu-1. A nit-2 nonsense mutant was isolated which has altered regulatory properties for control of nitrate reductase. L-amino acid oxidase, and uricase, and which may encode a truncated regulatory protein. Four nit-3 nonsense mutations were isolated, each of which completely lacks nitrate reductase activity, which is restored to markedly different levels by suppression with Ssu-1. Studies of heat activation and thermal lability of nitrate reductase suggest a qualitative alteration of the enzyme occurs in two of the Ssu-1 nit-3 strains.
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PMID:Amber nonsense mutations in regulatory and structural genes of the nitrogen control circuit of Neurospora crassa. 296 95

During growth of Aspergillus nidulans in medium containing ammonium the specific activities of most enzymes involved in catabolism of nitrogen sources are low (ammonium repression). The gdhA10 lesion, which results in loss of nicotinamide adenine dinucleotide phosphate-linked glutamate dehydrogenase activity, has been shown to lead to partial relief of ammonium repression of three amidase enzymes as well as histidase. The areA102 lesion led to altered levels of these enzymes but did not greatly affect ammonium repression. The double mutant areA102,gdhA10 was almost completely insensitive to ammonium repression of two of the amidase enzymes and histidase. This suggests that an interaction between the areA and gdhA genes in determining responses to ammonium occurs. Growth of mycelium in medium containing l-glutamate has been found to result in lowered levels of all four enzymes, and this occurs in strains insensitive to ammonium repression. Very strong repression in all strains occurred during growth in medium containing l-glutamine. Relief of these repressive effects of glutamate and glutamine was blocked by cycloheximide. Glutamate and glutamine had similar effects on the production of extracellular protease activity, and growth on glutamine led to low levels of urate oxidase. In contrast to the above enzymes, nitrate reductase was insensitive to the effects of glutamine and glutamate, even though this enzyme is very sensitive to ammonium repression. Although other possibilities exist, it is suggested that there may be mechanisms of general control of nitrogen-catabolic enzymes other than ammonium repression.
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PMID:Effects of ammonium, L-glutamate, and L-glutamine on nitrogen catabolism in Aspergillus nidulans. 461 4

In Aspergillus nidulans the positive-acting, wide domain regulatory gene areA mediates nitrogen metabolite repression. Previous analysis demonstrated that the C-terminal 153 residues of the areA product (AREA) are inessential for at least partial expression of most genes subject to regulation by areA. Paradoxically, areAr2, a -1 frameshift replacing the wild-type 122 C-terminal residues with a mutant peptide of 117 amino acids, leads to general loss of function. To determine the basis for the areAr2 mutant phenotype, and as a means of delineating functional domains within the C-terminal region of AREA, we have selected and characterised areAr2 revertants. Deletion analysis, utilising direct gene replacement, extended this analysis. A mutant areA product truncated immediately after the last residue of the highly conserved GATA (DNA-binding) domain retains partial function. The areAr2 product retains some function with respect to the expression of uaZ (encoding urate oxidase) and the mutant allele is partially dominant with respect to nitrate reductase levels. Consistent with the areAr2 product having a debilitating biological activity, we have demonstrated that a polypeptide containing both the wild-type DNA-binding domain and the mutant C-terminus of AREA2 is able to bind DNA in vitro but no longer shows specificity for GATA sequences.
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PMID:Mutational analysis of the C-terminal region of AREA, the transcription factor mediating nitrogen metabolite repression in Aspergillus nidulans. 856 80