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Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A 74-kDa iron-regulated outer membrane protein of Vibrio cholerae acts as the receptor for the V. cholerae iron-siderophore complex, ferric vibriobactin. MBG14, a mutant of V. cholerae 0395 containing a TnphoA insertion in a gene designated viuA, lacks this 74-kDa outer membrane protein and is unable to bind or utilize exogenous ferric vibriobactin. Introduction of a plasmid containing the complete viuA coding sequence and 513 bp of upstream DNA into MBG14 restored ferric vibriobactin utilization to the mutant. The DNA insert in this plasmid was sequenced, revealing a single open reading frame of 2,061 bp, encoding a deduced protein of 687 amino acids with a predicted molecular mass of 76,417 Da and a predicted initial signal sequence of 37 amino acids. ViuA showed only weak homology to two iron-regulated outer membrane proteins in Escherichia coli, IutA and FecA. Construction of viuA::TnphoA gene fusions allowed study of the regulation of viuA expression by iron. This regulation in E. coli was dependent on the fur gene. Northern (RNA) blot analysis of RNA from wild-type V. cholerae grown in high- and low-iron media revealed a monocistronic viuA message that was negatively regulated by iron at the transcriptional level. Primer extension analysis identified a single transcriptional start site, located 243 bp above the translational start site. The promoter region of viuA contained two interrupted dyad symmetric nucleotide sequences, overlapping the -10 and -35 boxes, each similar to the E. coli Fur binding consensus sequence. Another iron-regulated gene in V. cholerae that is negatively regulated by fur, irgA, requires a positive transcriptional activator (irgB) for expression. However, a strain of V. cholerae mutant in irgB was unaffected in viuA expression. These studies suggest that there is conserved, global coordinate iron regulation in V. cholerae by fur; additional regulatory factors, superimposed upon the fur system, may provide more precise control of individual iron-regulated genes.
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PMID:Cloning, sequencing, and transcriptional regulation of viuA, the gene encoding the ferric vibriobactin receptor of Vibrio cholerae. 131 81

We have selected for genes that, when present in multiple copies, enhance growth of wild-type cells of Saccharomyces cerevisiae in an iron-limiting medium. A gene designated FUP1, for 'ferric utilization proficient', was isolated by this approach. Increased dosage of FUP1 reduces the concentration of iron in the medium required for efficient growth and confers elevated levels of iron uptake activity in iron-limited cells. Disruption of the FUP1 locus reduces wild-type iron uptake rates by 2-fold in cells grown on raffinose medium but has no effect on glucose-grown cells. DNA sequencing showed that FUP1 encodes a hydrophilic 43 kDa protein identical to MSN1, a gene encoding a transcriptional activator implicated in carbon source regulation. Our results suggest that FUP1/MSN1 also regulates synthesis of gene products involved in iron uptake.
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PMID:Increased dosage of a transcriptional activator gene enhances iron-limited growth of Saccharomyces cerevisiae. 156 45

An iron-regulated promoter was cloned on a 2.1 kb Bg/II fragment from Pseudomonas sp. strain M114 and fused to the lacZ reporter gene. Iron-regulated lacZ expression from the resulting construct (pSP1) in strain M114 was mediated via the Fur-like repressor which also regulates siderophore production in this strain. A 390 bp StuI-PstI internal fragment contained the necessary information for iron-regulated promoter expression. This fragment was sequenced and the initiation point for transcription was determined by primer extension analysis. The region directly upstream of the transcription start point contained no significant homology to known promoter consensus sequences. However the -16 to -25 bp region contained homology to four other iron-regulated pseudomonad promoters. Deletion of bases downstream from the transcriptional start did not affect the iron-regulated expression of the promoter. The -37 and -43 bp regions exhibited some homology to the 19 bp Escherichia coli Fur-binding consensus sequence. When expressed in E. coli (via a cloned transacting factor from strain M114) lacZ expression from pSP1 was found to be regulated by iron. A region of greater than 77 bases but less than 131 upstream from the transcriptional start was found to be necessary for promoter activity, further suggesting that a transcriptional activator may be required for expression.
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PMID:Regulation of iron assimilation: nucleotide sequence analysis of an iron-regulated promoter from a fluorescent pseudomonad. 167 22

We have previously described a virulence gene in Vibrio cholerae (irgA) that is more than 850-fold regulated in response to iron. Negative regulation of irgA by iron occurred at the transcriptional level, and there was a dyad symmetric nucleotide sequence in the vicinity of the irgA promoter homologous to the Fur binding site in Escherichia coli. When irgA was cloned into E. coli, we showed that transcription of irgA required 900 base pairs of DNA upstream of the irgA promoter that contained an open reading frame in inverse orientation to irgA. In the present study, we show that this upstream region of DNA encodes a gene in inverse orientation to irgA (named irgB) that is also negatively regulated by iron. Insertional inactivation of irgB on the V. cholerae chromosome leads to loss of expression of a chromosomal irgA'-'phoA fusion (in which the primes indicate truncated genes), which is restored to normal by provision of irgB on a plasmid in trans. DNA sequencing of irgB shows that the protein product (IrgB) is homologous to the LysR family of positive transcriptional activators, and secondary structure analysis of IrgB predicts a helix-turn-helix DNA binding motif. The promoters of irgB and irgA are divergent but overlap each other and the previously defined Fur-binding site. We propose a model for iron regulation of irgA expression in V. cholerae. In the presence of sufficient iron, transcription of both irgA and irgB is negatively regulated by a Fur-like protein. In low iron conditions, negative regulation of transcription is removed, and production of IrgB leads to positive transcriptional activation of irgA. It seems likely that the high induction ratio of irgA expression under low- and high-iron conditions (850-fold) relates to the fact that its cognate positive transcriptional activator (irgB) is itself negatively regulated by iron.
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PMID:Positive transcriptional regulation of an iron-regulated virulence gene in Vibrio cholerae. 170 25

The significance of intracellular iron levels of Escherichia coli on the expression of the fumarate reductase operon (frd), which is regulated by the transcriptional activator FNR, was studied in vivo. The iron contents of aerobically and anaerobically grown E. coli were determined and related to the expression of frd and of genes (fiu, fepA, fhuF) which are regulated by the iron uptake regulatory protein Fur. The iron contents varied from 1.6 to 6.9 mumol Fe/g protein with no significant difference in aerobic and anaerobic bacteria. Expression of frd was not related to the different iron levels, but to oxygen supply. Only severe iron limitation in iron-depleted medium, which caused lower iron contents (0.8 to 1.6 mumol/g), reduced the expression of frd under anaerobic conditions. On the other hand, expression of fiu, fepA and fhuF clearly responded to iron supply and cellular content, but only slightly to changed O2 supply. Generally, expression of frd responded only to much stricter iron limitation, than expression of Fur regulated genes. It is concluded that the functional state of FNR during aerobic/anaerobic switch is not regulated by iron content and reversible binding of Fe2+ under physiological conditions. Therefore FNR does not communicate with the iron pool regulating the Fur protein.
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PMID:Iron content and FNR-dependent gene regulation in Escherichia coli. 180 64

We have identified a 110-kDa polypeptide that has a trans-acting regulatory activity on the expression of the pJM1 plasmid iron-uptake genes in Vibrio anguillarum. This protein is encoded by the angR gene and maps in a 3.6-kilobase-pair pJM1 DNA region located downstream of the iron transport genes. Full expression of this gene occurs under iron-limiting conditions and requires a 2.9-kilobase-pair upstream region in cis that maps within the coding region of the OM2 outer membrane protein, essential for the transport of iron into the cell cytosol. Determination of the siderophore anguibactin levels as well as analysis of specific transcripts for anguibactin biosynthetic genes demonstrated that AngR and another transcriptional activator, Taf, regulate in a synergistic fashion the level of anguibactin production by activation of transcription of the anguibactin biosynthetic genes under iron-limiting conditions.
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PMID:Regulation of the iron uptake system in Vibrio anguillarum: evidence for a cooperative effect between two transcriptional activators. 254 36

SoxR protein governs the soxRS (superoxide response) regulon of Escherichia coli by becoming a transcriptional activator when the cells are exposed to compounds that mediate univalent redox reactions, many of which produce superoxide as a by-product. SoxR was overproduced and purified to near homogeneity from a strain bearing an expression vector. It could bind specifically to the soxS operator even in the absence of RNA polymerase. The aerobically purified protein, which is readily autooxidized, could activate the transcription of soxS DNA even without exposure to known inducing agents. SoxR is a globular homodimer. It contains one [2Fe-2S] cluster per polypeptide chain, as demonstrated by optical and EPR spectroscopy combined with stoichiometric analysis of iron content, unpaired-electron-spin density, and reduction by dithionite. The protein is active in its oxidized ([2Fe-2S]2+) state. The presence of a prosthetic group capable of univalent redox reactions may help to explain the activation of the regulon in vivo by compounds that can mediate such reactions.
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PMID:Overproduction and physical characterization of SoxR, a [2Fe-2S] protein that governs an oxidative response regulon in Escherichia coli. 773 Mar 38

Many bacteria respond to a lack of iron in the environment by synthesizing siderophores, which act as iron-scavenging compounds. Fluorescent pseudomonads synthesize strain-specific but chemically related siderophores called pyoverdines or pseudobactins. We have investigated the mechanisms by which iron controls expression of genes involved in pyoverdine metabolism in Pseudomonas aeruginosa. Transcription of these genes is repressed by the presence of iron in the growth medium. Three promoters from these genes were cloned and the activities of the promoters were dependent on the amounts of iron in the growth media. Two of the promoters were sequenced and the transcriptional start site were identified by S1 nuclease analysis. Sequences similar to the consensus binding site for the Fur repressor protein, which controls expression of iron-repressible genes in several gram-negative species, were not present in the promoters, suggesting that they are unlikely to have a high affinity for Fur. However, comparison of the promoter sequences with those of iron-regulated genes from other Pseudomonas species and also the iron-regulated exotoxin gene of P. aeruginosa allowed identification of a shared sequence element, with the consensus sequence (G/C)CTAAAT-CCC, which is likely to act as a binding site for a transcriptional activator protein. Mutations in this sequence greatly reduced the activities of the promoters characterized here as well as those of other iron-regulated promoters. The requirement for this motif in the promoters of iron-regulated genes of different Pseudomonas species indicates that similar mechanisms are likely to be involved in controlling expression of a range of iron-regulated genes in pseudomonads.
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PMID:Identification of a DNA sequence motif required for expression of iron-regulated genes in pseudomonads. 789 66

The cloned Pseudomonas aeruginosa fur (ferric uptake regulator) gene was overexpressed in P. aeruginosa by using a T7 expression system, and the Fur protein (PA-Fur) was purified by using a combination of ion-exchange chromatography and metal affinity chromatography. The DNA binding activity of the PA-Fur protein was confirmed by gel mobility shift assays and DNase I footprints of the synthetic DNA fragment GATAAT GATAATCATTATC, representing a perfect "Fur box". In addition, it was shown that PA-Fur is capable of binding to promoter and operator determinants of the tightly iron-regulated Escherichia coli fepA-fes enterobactin gene system. The activity of PA-Fur on the promoters of iron-regulated genes involved in the production of two siderophores, pyochelin and pyoverdin, and in the expression of exotoxin A was investigated. Data indicating that the promoters of the pchR gene, encoding a transcriptional activator for pyochelin synthesis, and of the pvdS gene, encoding a positive regulator for pyoverdin production, are specifically recognized by Fur-Fe(II) are presented, suggesting that PA-Fur represses expression of pchR and pvdS during growth in an iron-replete environment. However, neither the promoter region of the gene encoding exotoxin A (toxA) nor the promoters of the regAB operon, required for toxA expression, interacted with high concentrations of purified PA-Fur. These data indicate that iron regulation of exotoxin A production involves additional factors which may ultimately be under the control of PA-Fur.
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PMID:Role of the ferric uptake regulator of Pseudomonas aeruginosa in the regulation of siderophores and exotoxin A expression: purification and activity on iron-regulated promoters. 852 28

SoxR is a transcriptional activator that senses superoxide and nitric oxide stress in Escherichia coli. The active protein isolated from E. coli contains a pair of [2Fe-2S] clusters per SoxR dimer. We previously demonstrated that the iron-free protein (apo-SoxR), isolated during purification in thiol-containing buffers, binds soxS promoter DNA with an affinity equal to that of the metalloprotein (Fe-SoxR), but lacks significant ability to activate transcription in vitro. Here we demonstrate the reversibility of this process: the full transcriptional activity of SoxR can be restored by in vitro assembly of iron-sulfur clusters into the apoprotein. Two methods were used to synthesize the metallocenters of SoxR: (i) nonenzymatic, in which apo-SoxR, incubated in the presence of iron, inorganic sulfide, and a reducing agent, regained full transcriptional activity in 5-6 h; (ii) enzymatic, in which NifS protein of Azotobacter vinelandii regenerated active Fe-SoxR in as little as 2 min. Analysis by electron paramagnetic resonance spectroscopy indicated that binuclear [2Fe-2S] clusters were restored by both the enzymatic and nonenzymatic reconstitutions. A mutant SoxR protein missing one of its four cysteine residues failed to undergo either transcriptional activation or the formation of [2Fe-2S] centers, even in the presence of NifS. Thus, only the presence of an iron-sulfur center is required to restore transcriptional activity to apo-SoxR. Moreover, the catalytic generation of [2Fe-2S] centers extends the known specificity of this enzyme beyond that already shown for [4Fe-4S] centers. Catalytic generation of [2Fe-2S]-containing SoxR could allow for rapid activation of this transcription factor in vivo.
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PMID:Activation of SoxR-dependent transcription in vitro by noncatalytic or NifS-mediated assembly of [2Fe-2S] clusters into apo-SoxR. 863 39


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