Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.7.1.1 (nitrate reductase)
3,728 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The chlD gene in Escherichia coli is required for the incorporation and utilization of molybdenum when the cells are grown with low concentrations of molybdate. We constructed chlD-lac operon fusions and measured expression of the fusion, Mo cofactor, and nitrate reductase activities under a variety of growth conditions. The chlD-lac fusion was highly expressed when cells were grown with less than 10 nm molybdate. Increasing concentrations of molybdate caused loss of activity, with less than 5% of the activity remaining at 500 nM molybdate; when tungstate replaced molybdate, it had an identical affect on chlD expression. Expression of chlD-lac was increased in cells grown with nitrate. Strains with chlD-lac plus an additional mutation in a chl or nar gene were constructed to test whether the regulation of chlD-lac required the concerted action of gene products involved with Mo cofactor or nitrate reductase synthesis. Mutations in narL prevented the increase in activity in response to nitrate; mutations in chlB, narC, or narI resulted in partial constitutive expression of the chlD-lac fusion: the fusion was regulated by molybdate, but it no longer required the presence of nitrate for maximal activity. Mutations in chlA, chlE, or chlG which affect Mo cofactor metabolism, did not affect the expression of chlD-lac.
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PMID:Molybdenum-sensitive transcriptional regulation of the chlD locus of Escherichia coli. 310 22

Nitrate reductase, encoded by the nar operon in Escherichia coli, is produced only under anaerobic conditions and induced to its maximum level in the presence of nitrate. The anaerobic expression of the nar operon depends on the fnr gene product (Fnr), and the stimulation of anaerobic expression by nitrate requires the narL gene product (NarL). Distinct regulatory domains within the nar promoter are involved in these two responses. The specific locations of the sequences required for these two regulatory mechanisms were identified by analysis of a detailed set of deletions extending into the regulatory region of the nar operon from the 5' end. A region located around -55 base pairs (bp) from the transcriptional start site and immediately upstream from the presumed RNA polymerase binding site was required for the response to Fnr and anaerobic conditions. A base sequence no longer than 27 bp, located at about -200 bp, was essential for the stimulation by nitrate coupled with NarL. This NarL-specific sequence was equally effective if positioned 10 or 11 bp further upstream or downstream from its wild type position. However, it was ineffective if positioned 4, 6, or 14 bp or greater distances either upstream or downstream. Apparent autoregulation by active nitrate reductase occurred in all 5'-deletion constructions which retained the Fnr response, indicating that this regulatory phenomenon involves sequences located no further than -64 bp from the transcription start site.
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PMID:Location of sequences in the nar promoter of Escherichia coli required for regulation by Fnr and NarL. 313 37

The nar operon, which encodes the three subunits of nitrate reductase in Escherichia coli, is fully induced under anaerobic conditions with nitrate. Two distinct regulatory domains have been delineated in the 5' region of the operon which respond respectively to positive induction by the fnr gene product under anaerobic conditions and to positive induction by the narL gene product in the presence of nitrate (S.F. Li, T. Rabi, and J.A. DeMoss, J. Bacteriol. 164:25-32). To characterize these two regulatory regions, we determined the DNA sequence for a 500-base-pair (bp) region extending upstream from the first structural gene of the nar operon. Analysis of subsequent subclones of the operon established that the 5' limit of the nar operon lies between 215 and 260 bp upstream from the translational start site of the first structural gene. The region required for induction by the fnr gene product is located within 160 bp from the translation start site, while the region responding to induction by nitrate extends an additional 100 bp upstream. Protein fusions of lacZ with the N-terminal sequence of the narG gene were constructed so that beta-galactosidase formation was under the control of the nar promoter and one or both regulatory domains. Analysis of strains bearing these fusion plasmids indicated that the expression of the hybrid proteins paralleled that of nitrate reductase by the parent plasmids, demonstrating that the regulatory signals did not extend significantly into the first structural gene. The transcriptional start site and the level of the transcription were determined by the S1 mapping procedure. One major transcript was identified which initiated -50 bp from the translational start site of the first structural gene. The synthesis of the transcript was repressed aerobically, was fully induced by nitrate anaerobically, and was greatly reduced in an Fnr- mutant. Possible regulatory sequences were identified in the 200-bp regulatory region extending upstream from the transcription start site.
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PMID:Promoter region of the nar operon of Escherichia coli: nucleotide sequence and transcription initiation signals. 330 46

Two nitrate reductase (NaR)-deficient mutants of pea (Pisum sativum L.), E1 and A300, both disturbed in the molybdenum cofactor function and isolated, respectively, from cv Rondo and cv Juneau, were tested for allelism and were compared in biochemical and growth characteristics. The F1 plants of the cross E1 X A300 possessed NaR and xanthine dehydrogenase (XDH) activities comparable to those of the wild types, indicating that these mutants belong to different complementation groups, representing two different loci. Therefore, mutant E1 represents, besides mutant A300 and the allelic mutants A317 and A334, a third locus governing NaR and is assigned the gene destignation nar 3. In comparison with the wild types, cytochrome c reductase activity was increased in both mutants. The mutants had different cytochrome c reductase distribution patterns, indicating that mutant A300 could be disturbed in the ability to dimerize NaR apoprotein monomers, and mutant E1 in the catalytic function of the molybdenum cofactor. In growth characteristics studied, A300 did not differ from the wild types, whereas fully grown leaves of mutant E1 became necrotic in soil and in liquid media containing nitrate.
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PMID:Biochemical and genetic comparison of two nitrate reductase-deficient pea mutants disturbed in the cofactor. 347 18

The three enzymes of the arginine deiminase pathway in Pseudomonas aeruginosa strain PAO were induced strongly (50- to 100-fold) by a shift from aerobic growth conditions to very low oxygen tension. Arginine in the culture medium was not essential for induction, but increased the maximum enzyme levels twofold. The induction of the three enzymes arginine deiminase (EC 3.5.3.6), catabolic ornithine carbamoyltransferase (EC 2.1.3.3), and carbamate kinase (EC 2.7.2.3) appeared to be coordinate. Catabolic ornithine carbamoyltransferase was studied in most detail. Nitrate and nitrite, which can replace oxygen as terminal electron acceptors in P. aeruginosa, partially prevented enzyme induction by low oxygen tension in the wild-type strain, but not in nar (nitrate reductase-negative) mutants. Glucose was found to exert catabolite repression of the deiminase pathway. Generally, conditions of stress, such as depletion of the carbon and energy source or the phosphate source, resulted in induced synthesis of catabolic ornithine carbamoyltransferase. The induction of the deiminase pathway is thought to mobilize intra- and extracellular reserves of arginine, which is used as a source of adenosine 5'-triphosphate in the absence of respiration.
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PMID:Regulation of enzyme synthesis in the arginine deiminase pathway of Pseudomonas aeruginosa. 625 88

To clone the nar operon of Escherichia coli without an effective selection procedure for the nar+ phenotype, a strategy utilizing nar::Tn5 mutants was employed. Partial segments of the nar operon containing Tn5 insertions were cloned into plasmid pBR322 by using the transposon resistance character for selection. A hybrid plasmid was constructed in vitro from two of these plasmids and isolated by a procedure that involved screening a population of transformed nar(Ts) mutant TS9A for expression of thermal stable nitrate reductase activity. A detailed restriction site map of the resulting plasmid, pSR95, corresponded closely to the composite restriction endonuclease map deduced for the nar region from maps of the cloned nar::Tn5 fragments. When transformed with pSR95, wild-type strain PK27 overproduced the alpha, beta, and gamma subunits of nitrate reductase, although nitrate reductase activity was only slightly increased. The alpha and beta subunits were overproduced about 5- to 10-fold and accumulated mostly as an inactive aggregate in the cytoplasm; the gamma subunit overproduction was detected as a threefold increase in the specific content of cytochrome b555 in the membrane fraction. Functional nitrate reductase and the cytochrome spectrum associated with functional nitrate reductase were restored in the nar::Tn5 mutant EE1 after transformation with pSR95. Although the specific activity of nitrate reductase in this case was less than that of the wild type, both the alpha and beta subunits appeared to be overproduced in an inactive form. In both strains PK27(pSR95) and EE1(pSR95), the formation of nitrate reductase activity and the accumulation of inactive subunits were repressed during aerobic growth. From these observations and the accumulation of inactive subunits were repressed during aerobic growth. From these observations and the demonstration that pSR95 contains a functional nor operon that encodes the alpha, beta, gamma subunits of nitrate reductase.
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PMID:Construction in vitro of a cloned nar operon from Escherichia coli. 633 27

Mud1 insertion mutants of Escherichia coli were obtained in which the lac structural genes were fused to the promoter of torA, a gene encoding the trimethylamine N-oxide (TMAO) reductase. Expression of the fusion is induced by TMAO and repressed by oxygen. However, in contrast to the nar operon which codes for the nitrate reductase structural genes, the tor::Mud1 fusion was found to be independent of the positive control exerted by the nirR gene product and not repressed by the molybdenum cofactor. The torA gene which is strongly linked to pyrF (28.3U) is different from any tor gene already described in E. coli or in Salmonella typhimurium.
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PMID:Regulation of the trimethylamine N-oxide (TMAO) reductase in Escherichia coli: analysis of tor::Mud1 operon fusion. 638 91

Seven known genes control Pseudomonas aeruginosa nitrate assimilation. Three of the genes, designated nas, are required for the synthesis of assimilatory nitrate reductase: nasC encodes a structural component of the enzyme; nasA and nasB encode products that participate in the biosynthesis of the molybdenum cofactor of the enzyme. A fourth gene (nis) is required for the synthesis of assimilatory nitrite reductase. The remaining three genes (ntmA, ntmB, and ntmC) control the assimilation of a number of nitrogen sources. The nas genes and two ntm genes have been located on the chromosome and are well separated from the known nar genes which encode synthesis of dissimilatory nitrate reductase. Our data support the previous conclusion that P. aeruginosa has two distinct nitrate reductase systems, one for the assimilation of nitrate and one for its dissimilation.
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PMID:Chromosomal location and function of genes affecting Pseudomonas aeruginosa nitrate assimilation. 642 Mar 93

We examined the properties of mutants of E. coli which are defective with respect to nitrate reductase activity. chlE::Mu cts and chlG::Mu cts mutants were all chlorate resistant, and the strains that we examined all synthesized nitrate reductase apoenzyme. We concluded that the chlE and chlG loci, like the chlA, chlB, and chlD loci, are involved in the synthesis of insertion of molybdenum cofactor. We identified at least four distinct phenotypic classes of chlC::Tn10 mutants, all of which were fully or partially sensitive to chlorate. Two of these classes may represent lesions in the structural genes for nitrate reductase subunits A and C. Two other classes may be altered in the regulation of the expression of nitrate reductase or other anaerobic enzymes. We propose the mnemonic nar for naming individual genes within the chlC locus.
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PMID:Nitrate reductase in Escherichia coli K-12: involvement of chlC, chlE, and chlG loci. 704 97

The mRNA accumulation pattern of the Chlamydomonas reinhardtii nitrate assimilation-related gene cluster has been elucidated. In ammonium-grown wild-type cells, nit-1 (nitrate reductase, NR), nar-1, nar-2 and nar-3 (nitrate transporter) genes showed very similar kinetics of expression when transferred to nitrate medium. Transcripts of all these genes accumulated transiently in ammonium-grown wild-type cells after a one-hour incubation in nitrogen-free medium, and practically disappeared at about 2 hours. Mutant strains lacking functional nitrate reductase showed similar accumulation kinetics of these transcripts during both nitrate induction and derepression in nitrogen-free media. In contrast to the other nar transcripts, that nar-4, a gene sharing similar sequences with nar-3, accumulated in small amounts in wild-type cells, and only increased after a long nitrate induction period. Nitrate and light showed a strong positive effect on the accumulation of nit-1 gene transcripts. Acetate as a carbon source allowed accumulation of nit-1 mRNA in the dark, indicating the existence of interactions between light and carbon metabolism in nit-1 gene expression. Our data strongly suggest that NR negatively autoregulates its own expression and that of nar genes.
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PMID:Expression of nitrate assimilation related genes in Chlamydomonas reinhardtii. 811 Oct 16


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