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

The ability of Ralstonia solanacearum to cause disease on plants depends on its type III secretion system (TTSS) encoded by hrp genes. The expression of hrp genes and known TTSS substrates is coordinately regulated by HrpB, a member of the AraC family of transcriptional regulators. Two HrpB-regulated promoters (hrpY and popABC) were characterized by deletion analysis, and the HrpB-dependent activation of these promoters was found to be conferred by a 25-nucleotide DNA element, the hrp(II) box (TTCGn16TTCG), which is present in other hrp promoters. The hrp(II) box element is an imperfect plant inducible promoter box, an element which was originally found in hrp promoters of Xanthomonas campestris (S. Fenselau and U. Bonas, Mol. Plant-Microbe Interact. 8:845-854, 1995) but which was not characterized at the molecular level. Site-directed mutagenesis showed that the hrp(II) box is essential for hrpY promoter activation in vivo. Functional analysis of the hrp(II) box element identified critical parameters that are required for HrpB-dependent activity. Further mapping analyses of several other hrpB-dependent promoters also indicated that the position of the hrp(II) box is conserved, at -70 to -47 bp from the transcriptional start. As a first step toward identifying novel TTSS effectors, we used the hrp(II) box consensus sequence to search for potential HrpB-regulated promoters in the complete genome sequence of R. solanacearum strain GMI1000. Among the 114 genes identified, a subset of promoters was found to have a structural relationship with hrp promoters, thus providing a pool of candidate genes encoding TTSS effectors.
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PMID:Characterization of the cis-acting regulatory element controlling HrpB-mediated activation of the type III secretion system and effector genes in Ralstonia solanacearum. 1506 33

The chitobiose operon, chbBCARFG, encodes genes for the transport and degradation of the N-acetylglucosamine disaccharide, chitobiose. Chitobiose is transported by the phosphotransferase system (PTS) producing chitobiose-6P which is hydrolysed to GlcNAc-6P by the chbF gene product and then further degraded by the nagBA gene products. Expression of the chb operon is repressed by NagC, which regulates genes involved in amino sugar metabolism. The inducer for NagC is GlcNAc-6P. NagC binds to two sites separated by 115 bp and the transcription start point of the chb operon lies within the downstream NagC operator. In addition the chb operon encodes its own specific regulator, ChbR, an AraC-type dual repressor-activator, which binds to two direct repeats of 19 bp located between the two NagC sites. ChbR is necessary for transcription activation in the presence of chitobiose in vivo. Induction of the operon also requires CAP, which binds to a site upstream of the ChbR repeats. In the absence of chitobiose both NagC and ChbR act as repressors. Together these three factors cooperate in switching chb expression from the repressed to the activated state. The need for two specific inducing signals, one for ChbR to activate the expression of the operon and a second for NagC to relieve its repression, ensure that the chb operon is only induced when there is sufficient flux through the combined chb-nag metabolic pathway to activate expression of both the chb and nag operons.
Mol Microbiol 2004 Apr
PMID:Expression of the chitobiose operon of Escherichia coli is regulated by three transcription factors: NagC, ChbR and CAP. 1506 32

Intact AraC protein is poorly soluble and difficult to purify, whereas its dimerization domain is the opposite. Unexpectedly, the DNA binding domain of AraC proved also to be soluble in cells when overproduced and is easily purified to homogeneity. The DNA binding affinity of the DNA binding domain for its binding site could not be measured by electrophoretic mobility shift because of its rapid association and dissociation rates, but its affinity could be measured with a fluorescence assay and was found to have a dissociation constant of 1 x 10(-8)M in 100 mM KCl. The binding of monomers of the DNA binding domain to adjacent half-sites occurs without substantial positive or negative cooperativity. A simple analysis relates the DNA binding affinities of monomers of DNA binding domain and normal dimeric AraC protein.
J Mol Biol 2004 Jul 16
PMID:Biochemical and physiological properties of the DNA binding domain of AraC protein. 1522 16

AdpA, belonging to the AraC/XylS family, is the key transcriptional activator for a number of genes of various functions in the A-factor regulatory cascade in Streptomyces griseus. It consists of a ThiJ/PfpI/DJ-1-like dimerization domain at its N-terminal portion and a DNA-binding domain with two helix-turn-helix motifs at its C-terminal portion, representing a large subgroup of the AraC/XylS family. Uracil interference assay and missing T and GA interference assays on several AdpA binding sites, followed by gel mobility shift assays on systematically mutated binding sites, revealed a consensus AdpA-binding sequence, 5'-TGGCSNGWWY-3' (S: G or C; W: A or T; Y: T or C; N: any nucleotide). A dimer of AdpA bound a site including the two consensus sequences, with a space of 13-14 bp, as an inverted repeat (type I) at various positions, for example more than 200 bp upstream (-200) and 25 bp downstream (+25) from the transcriptional start point of the target gene. In addition, AdpA also bound a site including the consensus sequence in a single copy (type II) at positions, in most cases, from -40 to -50 and from -50 to -60. For transcriptional activation, some genes required simultaneous binding of a dimer of AdpA to type I and II sites, but others required only a single type I or type II site. AdpA bound mutated type I sites with various distances between the two consensus sequences with significant affinities, although the optimal distances for AdpA to bind were 13-14 bp and 2 bp. The DNA-binding domain is therefore connected to the ThiJ/PfpI/DJ-1-like dimerization domain with a flexible linker. The DNA-binding specificity of AdpA in conjunction with that of other AraC/XylS family members is discussed.
Mol Microbiol 2004 Jul
PMID:DNA-binding specificity of AdpA, a transcriptional activator in the A-factor regulatory cascade in Streptomyces griseus. 1522 17

A number of AraC family transcriptional activators bind low-molecular-weight ligands that modulate the activity of these proteins. Recently, it has become clear that the activity of several virulence-related AraC family members is regulated through the direct interaction of protein ligands. These interactions, in general, function to activate or repress the transcription of virulence genes in response to specific extracellular stimuli. The identification and characterization of several protein ligands that modify the activity of AraC family members in Pseudomonas aeruginosa and Salmonella enterica are discussed herein.
Mol Microbiol 2004 Oct
PMID:Modulation of AraC family member activity by protein ligands. 1546 2

The mtr (multiple transferable resistance) gene complex in Neisseria gonorrhoeae encodes an energy-dependent efflux pump system that is responsible for export of anti-bacterial hydrophobic agents. Expression of the mtrCDE operon in gonococci is negatively regulated by the MtrR protein. Hydrophobic agent resistance mediated by the mtr system is also inducible, which results from an AraC-like protein termed MtrA. In this work, we identified and characterized a pump similar to the gonococcal mtr system in various strains of Neisseria meningitidis. Unlike the situation with gonococci, the mtr system in meningococci is not subject to the MtrR or MtrA regulatory schemes. An analysis of the promoter region of the mtrCDE operon in a panel of meningococcal strains revealed the presence of one or two classes of insertion sequence elements. A 155-159 bp insertion sequence element known as the Correia element, previously identified elsewhere in the gonococcal and meningococcal genomes, was present in the mtrCDE promoter region of all meningococcal strains tested. In addition to the Correia element, a minority of strains had a tandemly linked, intact copy of IS1301. As described previously, a binding site for the integration host factor (IHF) was present at the centre of the Correia element upstream of mtrCDE genes. IHF was found to bind specifically to this site and deletion of the IHF binding site enhanced mtrC transcription. We also identified a post-transcriptional regulation of the mtrCDE transcript by cleavage in the inverted repeat of the Correia element, as previously described by Mazzone et al. [Gene278: 211-222 (2001)] and De Gregorio et al. [Biochim Biophys Acta 1576: 39-44 (2002)]for other Correia element. We conclude that the mtr efflux system in meningococci is subject to transcriptional regulation by IHF and post-transcriptional regulation by cleavage in the inverted repeat of the Correia element.
Mol Microbiol 2004 Nov
PMID:Modulation of the mtrCDE-encoded efflux pump gene complex of Neisseria meningitidis due to a Correia element insertion sequence. 1549 63

As in many other Gram-negative phytopathogenic bacteria, the Hrp type III secretion system is essential for the pathogenicity of Ralstonia solanacearum on host plants. The expression of most of the type III effector genes previously isolated from R. solanacearum is co-regulated with those of hrp genes by an AraC-type transcriptional activator, HrpB. In order to isolate type III-related pathogenicity genes, we screened hrpB-regulated genes in R. solanacearum. Using a transposon-based system, we isolated 30 novel hpx (hrpB-dependent expression) genes outside the hrp gene cluster. Most of the hpx genes contain a PIP (plant-inducible promoter) box-like motif in their putative promoter regions. Seven hpx genes encoded homologues of known type III effectors and type III-related proteins found in other animal and plant pathogens. Four encoded known enzymes, namely, glyoxalase I, Nudix hydrolase, spermidine synthase and transposase. Interestingly, six hpx genes encoded two types of leucine-rich repeat (LRR) protein. Products of the remaining genes did not show any significant homology to known proteins. We also identified two novel hrpB-regulated genes, hpaZ and hpaB, downstream of hrpY in the hrp cluster. The hpaB gene of R. solanacearum, but not hpaZ, was required for both the pathogenicity and ability to induce hypersensitive reaction on plants. We show that a hpaB null mutant still produces Hrp pili on the cell surface although it shows a typical Hrp-defective phenotype on plants.
Mol Microbiol 2004 Nov
PMID:Genetic screening of Hrp type III-related pathogenicity genes controlled by the HrpB transcriptional activator in Ralstonia solanacearum. 1552 73

Ribonucleotide reductases (RNRs) catalyse the conversion of ribonucleotides to deoxyribonucleotides and are essential for de novo DNA synthesis and repair. Streptomyces spp. contain genes coding for two RNRs. We show here that the Streptomyces coelicolor M145 nrdAB genes encoding an oxygen-dependent class I RNR are co-transcribed with nrdS, which encodes an AraC-like regulatory protein. Likewise, the class II oxygen-independent RNR nrdJ gene forms an operon with a likely regulatory gene, nrdR, which encodes a protein possessing an ATP-cone domain like those present in the allosteric activity site of many class Ia RNRs. Deletions in nrdB and nrdJ had no discernible effect on growth individually, but abolition of both RNR systems, using hydroxyurea to inactivate the class Ia RNR (NrdAB) in the nrdJ deletion mutant, was lethal, establishing that S. coelicolor possesses just two functional RNR systems. The class II RNR (NrdJ) may function to provide a pool of deoxyribonucleotide precursors for DNA repair during oxygen limitation and/or for immediate growth after restoration of oxygen, as the nrdJ mutant was slower in growth recovery than the nrdB mutant or the parent strain. The class Ia and class II RNR genes show complex regulation. The nrdRJ genes were transcribed some five- to sixfold higher than the nrdABS genes in vegetative growth, but when nrdJ was deleted, nrdABS transcription was upregulated by 13-fold. In a reciprocal experiment, deletion of nrdB had little effect on nrdRJ transcription. Deletion of nrdR caused a dramatic increase in transcription of nrdJ and to a less extent nrdABS, whereas disruption of cobN, a gene required for synthesis of coenzyme B12 a cofactor for the class II RNR, caused similar upregulation of transcription of nrdRJ and nrdABS. In contrast, deletion of nrdS had no detectable effect on transcription of either set of RNR genes. These results establish the existence of control mechanisms that sense and regulate overall RNR gene expression.
Mol Microbiol 2004 Nov
PMID:Alternative oxygen-dependent and oxygen-independent ribonucleotide reductases in Streptomyces: cross-regulation and physiological role in response to oxygen limitation. 1552 84

The plasmid-encoded Per regulatory locus of enteropathogenic Escherichia coli (EPEC) is generally considered to consist of three genes, perA, perB and perC. PerA, a member of the AraC-like family of transcriptional regulators, is known to be an activator of its own promoter (autoactivation) as well as of the plasmid-located bfp operon encoding bundle-forming pili, but its role in activation of the chromosomal locus of enterocyte effacement (LEE) pathogenicity island, which confers the property of intimate adherence on EPEC, requires clarification. Here, we show that PerA is also required for activation of the master regulatory LEE operon, LEE1, but that this activation is indirect, being achieved via autoactivation of the per promoter which ensures sufficient production of the PerC protein to activate LEE1. In contrast, PerA-dependent activation of the per and bfp promoters is direct and does not require the other Per proteins, but is modulated by the nucleoid-associated protein H-NS. The closely related VirF regulator from Shigella flexneri cannot substitute for PerA to activate these promoters, despite being able to bind their upstream regions in vitro. PerA can bind the per and bfp promoter fragments to form multiple complexes, while VirF forms only a single complex. Site-directed mutagenesis of the PerA protein suggests that, like VirF, it may use both of its carboxy-terminal helix-turn-helix motifs for DNA interaction, and may also make direct contacts with RNA polymerase. In addition, we have isolated mutations in the poorly characterized amino-terminal domain of PerA which affect its ability to activate gene expression.
Mol Microbiol 2004 Nov
PMID:Direct and indirect transcriptional activation of virulence genes by an AraC-like protein, PerA from enteropathogenic Escherichia coli. 1552 91

The Yersinia pestis plasmid pCD1-encoded type III secretion system (T3SS) is essential for the pathogenicity of Y. pestis in mammalian hosts. T3SS-associated genes are maximally expressed at 37 degrees C in the absence of extracellular calcium. Expression of T3SS genes requires LcrF, an AraC-like transcriptional activator, and is repressed by YmoA, a small histone-like protein. The mechanism by which temperature regulates T3SS gene expression has not been determined; however, changes in DNA topology have been implicated in this process. We report here that a Y. pestis strain deficient in production of the ClpXP and Lon proteases does not express a functional T3SS partly because of high cytosolic levels of YmoA. YmoA is rapidly degraded at 37 degrees C in wild-type Y. pestis, but remains stable in a clpXPlon deletion mutant. The stability of YmoA in wild-type Y. pestis increased as the growth temperature of the culture decreased; in contrast, YmoA was stable at all temperatures examined in the clpXPlon deletion mutant. These results indicate that the ClpXP and Lon proteases contribute to the environmental regulation of the Y. pestis T3SS system through regulated proteolysis of YmoA.
Mol Microbiol 2004 Dec
PMID:The ATP-dependent ClpXP and Lon proteases regulate expression of the Yersinia pestis type III secretion system via regulated proteolysis of YmoA, a small histone-like protein. 1555 75


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