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Regulation and over-expression of the fnr gene of Escherichia coli 总被引:33,自引:0,他引:33
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FNR activates and represses transcription in vitro. 总被引:18,自引:0,他引:18
A D Sharrocks J Green J R Guest 《Proceedings. Biological sciences / The Royal Society》1991,245(1314):219-226
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Constantinidou C Hobman JL Griffiths L Patel MD Penn CW Cole JA Overton TW 《The Journal of biological chemistry》2006,281(8):4802-4815
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FNR and its role in oxygen-regulated gene expression in Escherichia coli 总被引:71,自引:0,他引:71
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Roles of SpoT and FNR in NH4+ assimilation and osmoregulation in GOGAT (glutamate synthase)-deficient mutants of Escherichia coli. 总被引:1,自引:0,他引:1
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An osmosensitive mutant of Escherichia coli was isolated and shown to harbor two mutations that were together necessary for osmosensitivity. One (ossB) was an insertion mutation in the gltBD operon, which encodes the enzyme glutamate synthase (GOGAT), involved in ammonia assimilation and L-glutamate biosynthesis. The other (ossA) was in the fnr gene, encoding the regulator protein FNR for anaerobic gene expression. Several missense or deletion mutations in fnr and gltBD behaved like ossA and ossB, respectively, in conferring osmosensitivity. A mutation affecting the DNA-binding domain of FNR was recessive to fnr+ with respect to the osmotolerance phenotype but was dominant-negative for its effect on expression of genes in anaerobic respiration. Our results may most simply be interpreted as suggesting the requirement for monomeric FNR during aerobic growth of E. coli in high-osmolarity media, presumably for L-glutamate accumulation via the GOGAT-independent pathway (catalyzed by glutamate dehydrogenase [GDH]), but the mechanism of FNR action is not known. We also found that the spoT gene (encoding guanosine 3',5'-bispyrophosphate [ppGpp] synthetase II/ppGpp-3' pyrophosphohydrolase), in multiple copies, overcomes the defect in NH4+ assimilation associated with GOGAT deficiency and thereby suppresses osmosensitivity in gltBD fnr strains. Enhancement of GDH activity in these derivatives appears to be responsible for the observed suppression. Its likely physiological relevance was established by the demonstration that growth of gltBD mutants (that are haploid for spoT+) on moderately low [NH4+] was restored with the use of C sources poorer than glucose in the medium. Our results raise the possibility that SpoT-mediated accumulation of ppGpp during C-limited growth leads to GDH activation and that the latter enzyme plays an important role in N assimilation in situ hitherto unrecognized from studies on laboratory-grown cultures. 相似文献
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Molecular genetic analysis of FNR-dependent promoters 总被引:38,自引:17,他引:21
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Regulation of narK gene expression in Escherichia coli in response to anaerobiosis, nitrate, iron, and molybdenum.
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The regulation of the narK gene in Escherichia coli was studied by constructing narK-lacZ gene and operon fusions and analyzing their expression in various mutant strains in response to changes in cell growth conditions. Expression of narK-lacZ was induced 110-fold by a shift to anaerobic growth and a further 8-fold by the presence of nitrate. The fnr gene product mediates this anaerobic response, while nitrate control is mediated by the narL, narX, and narQ gene products. The narX and narQ gene products were shown to sense nitrate independently of one another and could each activate narK expression in a NarL-dependent manner. We provide the first evidence that NarL and FNR interact to ensure optimal expression of narK. IHF and Fis proteins are also required for full activation of narK expression, and their roles in DNA bending are discussed. Finally, the availability of molybdate and iron ions is necessary for optimal narK expression, whereas the availability of nitrite is not. Although the role of the narK gene product in cell metabolism remains uncertain, the pattern of narK gene expression is consistent with a proposed role of NarK in nitrate uptake by the cell for nitrate-linked electron transport. 相似文献
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Actinobacillus pleuropneumoniae hlyX gene homology with the fnr gene of Escherichia coli. 总被引:12,自引:5,他引:7
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The hlyX gene from Actinobacillus pleuropneumoniae, which confers a hemolytic phenotype on Escherichia coli, was sequenced, and its role in regulation of gene expression was investigated. No similarity was found between the hlyX sequence and sequences of known hemolysin or cytotoxin genes. However, the hlyX sequence was very similar to that of the fnr gene of Escherichia coli which encodes the global regulatory protein, FNR. Comparison of the deduced amino acid sequence of the hlyX gene product (HlyX) with that of FNR revealed a high degree of well-aligned sequence correlation throughout the polypeptide chain. For example, 23 of 24 amino acids in the DNA-binding region of FNR are identical in the corresponding region of HlyX. Four cysteine residues in the amino-terminal region are also conserved. The promoter region of hlyX is very similar to that of fnr. It has a putative -10 sequence which closely resembles the E. coli -10 consensus sequence. This sequence is overlapped by a potential operator which is very similar to the FNR-binding-site consensus sequence. Functional homology between HlyX and FNR was also demonstrated. Plasmids carrying hlyX complemented the nutritional lesion of an fnr deletion strain of E. coli. These data suggest that HlyX may regulate, rather than mediate, hemolytic activity in E. coli, but the possibility that HlyX is both a regulator of gene expression and a hemolysin cannot be excluded. 相似文献
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Use of gene fusions to study the expression of fnr, the regulatory gene of anaerobic electron transfer in Escherichia coli 总被引:3,自引:0,他引:3
Marie-Claire Pascal Violaine Bonnefoy Michel Fons Marc Chippaux 《FEMS microbiology letters》1986,36(1):35-39
Abstract Fusions between fnr , the regulatory gene for anaerobic electron transfer, and lacZ were obtained by insertion of Mu d II1734 bacteriophage in the fnr gene cloned in a plasmid. After transfer onto the chromosome, study of the fusion showed that the expression of fnr is independent of anaerobiosis, negatively regulated by its own product and partly positively controlled by cyclic AMP. 相似文献
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To explore the oxygen response regulators involved in thiol peroxidase gene (tpx) expression in Escherichia coli, we constructed a single-copy tpx-lacZ operon fusion and monitored tpx-lacZ expression in various genetic backgrounds. Expression of the tpx-lacZ fusion was increased 4-fold by aerobic growth. Anaerobic expression of tpx-lacZ in either (delta)arcA or delta(fnr) strains was 2.5-fold depressed compared with that of the wild-type strain. The results of immunoblotting experiments also demonstrated that ArcA and Fnr regulatory proteins repressed thiol peroxidase gene expression during anaerobic growth. Inspection of the tpx promoter region revealed putative binding sites for ArcA and Fnr. It thus appears that ArcA and Fnr function as repressors by blocking the binding of RNA polymerase to the tpx promoter in E. coli under anaerobic growth conditions. 相似文献