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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Two rapid and convenient methods have been developed for the amplification and purification of FNR, the anaerobic transcription regulator of Escherichia coli. The overproduced proteins resemble wild-type FNR in their basic properties: oligomeric state, iron contents (up to 2.7 atoms per monomer), DNA-binding affinities and ability to activate transcription. However, unlike previous preparations, FNR could be isolated in a form containing up to 0.25 atoms of acid-labile sulphur per monomer. Incorporation of iron increased the Mr of FNR from 28,000 to 40,000. Under anaerobic conditions, reconstituted FNR exhibited absorption maxima at 315 nm and 420 nm, which were replaced by a broad absorbance from 380 to 440 nm under aerobic conditions. These observations indicate that FNR contains one redox-sensitive [3Fe 4S] or [4Fe 4S] centre per monomer. Footprints of FNR-dependent promoters (ansB, fdn, fnr, narG, pflP6, pflP7 and nirB) showed protection at all of the predicted FNR sites except the pflP7 (-57.5), ansB (-74.5) and nirB (-89.5) sites. An unpredicted second binding site was detected at -57.5 in the narG promoter. Hypersensitive sites within regions of FNR protection indicated that FNR bends DNA in a similar way to CRP. Promoters containing binding sites for FNR (FF), CRP (CC) or hybrid sites (CF or FC) were footprinted with FNR and two derivatives (FNR-610 and FNR-573) which activate the CCmelR promoter in vivo. FNR preferentially protected the FNR site (FF) whereas FNR-610 preferred CC and FNR-573 interacted with equal affinity at all sites.
Mol Microbiol 1996 Jan
PMID:FNR-DNA interactions at natural and semi-synthetic promoters. 882 42

The Escherichia coli DNA-binding protein FIS (factor for inversion stimulation) stimulates site-specific recombination reactions catalysed by DNA invertases and is an activator of stable RNA synthesis. To address the question of whether FIS is involved in other cellular processes we have identified and sequenced proteins whose expression pattern is affected by FIS. This has led to the identification of several E. coli genes whose expression in vivo is either enhanced or repressed by FIS. All of these genes encode enzymes or transport proteins involved in the catabolism of sugars or nucleic acids, and their expression is also dependent on the cAMP-CRP complex. In most cases studied the regulation by FIS is indirect and occurs through effects on the synthesis of the respective repressor proteins. We conclude that FIS is a transcriptional modulator involved in the regulation of metabolism in E. coli.
Mol Microbiol 1996 Oct
PMID:FIS is a regulator of metabolism in Escherichia coli. 889 5

The dimeric histone-like protein HU, one of the most abundant DNA binding proteins of Escherichia coli, is encoded by two closely related but unlinked genes, hupA and hupB. Overproduction of one or the other of the subunits has been shown to induce the SOS response and mucoidy. To understand how the synthesis of this protein is coordinated, we studied the transcription control of the two hup genes. We show here that CRP stimulated the transcription of both genes. In contrast, the FIS protein, one of the major positive regulators of the stable RNA operons, stimulated the transcription of the hupA gene, whereas it repressed that of the hupB gene. Moreover, stringent control, which like FIS also regulates the transcription of the stable RNA operons, affected the hupB transcription while it had no effect on hupA. This opposite regulation of the transcription of the two HU genes is reflected at the protein level signifying that changes in the composition of HU occur upon changes in the environment. It is rather unexpected that such divergent transcriptional regulation controls the two genes encoding a dimeric protein.
J Mol Biol 1996 Oct 25
PMID:Regulation of HU alpha and HU beta by CRP and FIS in Escherichia coli. 891 96

Activation of malEp and malKp, two divergent promoters from Escherichia coli, depends on the synergistic action of MalT and CRP. The reaction involves a common regulatory region located in between and comprising multiple binding elements for both regulatory proteins. The binding of MalT and CRP to this region is known to result in the formation of a higher-order structure that is responsible for malKp activation. This paper presents genetic data which together with previous results, provide compelling evidence that this higher-order structure is also responsible for malEp activation. The role(s) that this structure or elements thereof play in the activation of malEp is analysed by monitoring both the occupancy of the proximal MalT sites (sites 1 and 2) and the activity of different malEp variants in strains containing increasing amounts of active MalT. A truncated malEp promoter comprising only MalT sites 1 and 2 forms a minimal MalT-dependent promoter whose activity is limited by the occupancy of these sites. One role of the higher-order structure formed by MalT and CRP when bound to the entire regulatory region is to ensure high occupation of MalT sites 1 and 2, but it is not its only function. Some elements of this structure, namely the CRP site 1, located at -76.5, and the distal MalT sites, seem to play a direct role in malEp activation besides their participation in the assembly of the higher-order structure.
J Mol Biol 1996 Dec 20
PMID:On the role of the multiple regulatory elements involved in the activation of the Escherichia coli malEp promoter. 900 Jun 16

In CytR regulated promoters in Escherichia coli, the cAMP-CRP complex acts as a transcriptional activator as well as a co-repressor for the CytR protein. Repression by CytR depends on the formation of nucleoprotein complexes in which CytR binds cooperatively to the DNA with one or two cAMP-CRP complexes. Here, we demonstrate that in order to establish CytR regulation in a cAMP-CRP dependent class II promoter with a single CRP site (CRP site centred around position -40.5) in which the CytR operator is located upstream of the CRP site, high affinity binding sites for both regulators are required. The efficiency of CytR regulation was observed to be modulated by RNA polymerase (RNAP)-promoter interactions. Specifically, in class II promoters with a single CRP site, the efficiency of CytR regulation was found to correlate inversely with cAMP-CRP independent promoter activity. These observations can be reconciled in a competition model for CytR regulation in which CytR and RNAP compete for cooperative binding with cAMP-CRP to the promoters in vivo. In this model, two mutually exclusive ternary complexes can be formed: a CytR/cAMP-CRP/promoter repression complex and an RNAP/cAMP-CRP/promoter activation complex. Thus, CytR regulation critically depends on formation of a repression complex that binds the promoter with sufficiently high affinity to exclude formation of the competing activation complex. We suggest that the transition from repression to activation involves a switch in the protein-protein interactions made by cAMP-CRP from CytR to RNAP. On the basis of the regulatory features of the promoters analysed here, we speculate about the advantages offered by the structural complexity of natural CytR/cAMP-CRP regulated promoters.
J Mol Biol 1997 Mar 14
PMID:Design of CytR regulated, cAMP-CRP dependent class II promoters in Escherichia coli: RNA polymerase-promoter interactions modulate the efficiency of CytR repression. 908 66

We cloned and characterized the gntRKU operon encoding part of the GntI system involved in gluconate uptake and catabolism by Escherichia coli. The operon was shown to encode its repressor, a thermoresistant gluconate kinase, and a low affinity gluconate permease. CAT fusion analysis revealed that the operon has a promoter for gntR and another for gntKU, and that the gntR gene is constitutively expressed, while that of gntKU is regulated positively by the cAMP-CRP complex and negatively by GntR. Read-through transcription from the gntR promoter into gntK was decreased in the presence of GntR, although GntR did not repress its own promoter. In addition, transcriptional attenuation was observed after the gntK gene, so gntU expression is reduced presumably to modulate the production of the low affinity gluconate permease according to the available concentration of gluconate.
J Mol Biol 1997 Apr 11
PMID:Gene organization and transcriptional regulation of the gntRKU operon involved in gluconate uptake and catabolism of Escherichia coli. 913 11

Anaerobic expression of the focA pfl operon is dependent on the transcription factors ArcA and FNR and transcription is directed by multiple, anaerobically regulated promoters. A FNR-binding site is centred at -41.5 bp relative to the P6 promoter, inactivation of which severely impairs anaerobic expression of the complete operon. Mutations were introduced into this binding site to create a consensus recognition site for the cAMP-receptor protein, CRP (CC-site), and one that was recognised by both CRP and FNR (CF-site). Transcription directed by these mutant binding sites in vivo in different promoter constructs was analysed by primer extension and by constructing lacZ operon fusions. With a derivative including only the P6 promoter and the CF-binding site, transcription was shown to be independent of oxygen and was activated by CRP or FNR. In agreement with previous findings, FNR only activated transcription anaerobically. In a construct including the CC-binding site transcription was strong. CRP dependent and initiated at the identical site to the wild-type promoter. Transcription activation from the CC-site was exquisitely sensitive to low cAMP concentration. Surprisingly, in a crp mutant, anaerobically inducible, FNR-dependent transcription directed by the CC-site was detected, indicating that FNR can recognise a consensus CRP-binding site in vivo. A strain unable to synthesise CRP or FNR exhibited no transcription from the P6 promoter. Essentially the same results were observed in a series of constructs that also included the promoter P7 and its regulatory sequences. Evidence is also presented which demonstrates that CRP activates transcription from the natural FNR-binding site of the P6 promoter. In vitro DNA-binding studies showed that CRP specifically interacted with the FNR-binding site, protecting exactly the same sequence as that protected by the FNR protein. Interaction of CRP with the natural FNR-binding site was reduced greater than 50-fold compared to its interaction with the mutant CC-binding site. Although we could not demonstrate that FNR interacted with the CC-binding site in vitro, it did bind to the CF-site giving the same protection as observed with the wild-type FNR-binding site. FNR also activated transcription from the CF-site in vitro, giving further support to the idea that a single functional DNA half-site is sufficient to direct binding and transcription activation by a dimeric transcription factor.
Mol Microbiol 1997 Feb
PMID:Transcriptional activation by FNR and CRP: reciprocity of binding-site recognition. 915 53

Expression of the flagellar master operon, flhD, is known to be affected by growth conditions and by mutations in a variety of genes. In the present work, the transcriptional control of the Salmonella typhimurium flhD operon was investigated in various genetic backgrounds. First, we examined the effect of mutations in the global regulators cAMP-CRP, H-NS, OmpR and RpoS. Mutations in the cya, crp or hns gene reduced but did not eliminate flhD expression. However, expression was completely inhibited in the cya hns and crp hns double mutants. These results indicate that cAMP-CRP and H-NS independently activate the flhD operon and that maximal expression is attained in the presence of both regulators. On the other hand, the ompR and rpoS mutations did not affect either the motility phenotype or flhD expression. We next examined the expression of a chromosomal flhD-lac fusion gene in the presence of a plasmid carrying the wild-type flhD operon. It was found that under this condition the chromosomal flhD operon was repressed or activated, depending on the intracellular activity of FliA, an alternative sigma factor specific for late flagellar operons. In the absence of FliA or in the presence of both FliA and its cognate anti-sigma factor FlgM, the flhD operon was autogenously repressed, whereas in the flgM mutant background it was autogenously activated in the presence of FliA. This autoregulation was still observed in the crp or hns mutant background, indicating that the autogenous control is achieved by a mechanism that is independent of the cAMP-CRP and H-NS regulatory pathways.
Mol Gen Genet 1997 Apr 28
PMID:Autogenous and global control of the flagellar master operon, flhD, in Salmonella typhimurium. 918 Jun 98

The T cell response of C57BL/6 mice to human C-reactive protein (hCRP), an inducible acute phase protein, was analysed. Two I-A(b)-restricted epitopes at positions 79 95 (epitope A) and 87-102 (epitope B) were identified using a panel of CD4+ T cell clones. Human C-reactive protein shares considerable homology with mouse C-reactive protein and mouse serum amyloid P component. Interestingly, the two epitopes map to the region of lowest homology between human CRP and its mouse homologues. Human CRP-specific T cell clones express a restricted T cell receptor (TCR) repertoire, both with regard to usage of TCR germline gene segments (V alpha, J alpha, V beta, J beta) and certain TCR alpha beta combinations. Therefore, epitope-A specific clones preferentially use TCR V beta8.3 and V alpha3 J alpha15 V beta8.3-J beta2.3 and epitope-B specific clones use V beta2 and V alpha1-J alpha24/30-V beta2. This bias is even more pronounced when TCR usage is correlated with epitope fine specificity. A role for homology of hCRP to self components in selecting these particular T cell epitopes and TCR is discussed.
Mol Immunol 1997 Feb
PMID:The MHC class II-restricted T cell response of C57BL/6 mice to human C-reactive protein: homology to self and the selection of T cell epitopes and T cell receptors. 918 44

Many bacterial pathogens regulate the expression of virulence genes in a co-ordinate manner in response to changes in the environment. For example, the human pathogen, Vibrio cholerae, possesses a virulence regulon composed of over 20 genes involved in colonization, toxin production and bacterial survival within the host, which are co-ordinately regulated by external stimuli, such as temperature, pH and osmolarity. Although the expression of the regulon is dependent upon the transcriptional activator ToxR, most of these genes are controlled by a second transcriptional activator, ToxT, which is itself positively regulated by ToxR. The mechanisms by which environmental stimuli influence the ToxR regulon are not yet understood, but ToxR-mediated control over the expression of toxT clearly plays a role. The recent finding that the global regulator cAMP-CRP also influences the expression of the ToxR regulon under various environmental conditions raises new issues regarding the pathways and mechanisms by which this regulation is achieved and indicates that multiple overlapping systems are involved.
Mol Microbiol 1997 Sep
PMID:Control of the ToxR virulence regulon in Vibrio cholerae by environmental stimuli. 935 Aug 58


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