Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P51532 (transcriptional activator)
 6,546 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

High-risk human papillomaviruses are causally associated with cervical cancer. Two viral oncogenes, E6 and E7, are expressed in most cervical cancers, and these genes cause cancer when expressed in experimental animals. The E6 protein targets the p53 tumor suppressor for degradation, while the E7 protein inactivates the retinoblastoma susceptibility protein (pRb), in part by stimulating its degradation. In contrast, expression of E7 in the absence of E6 leads to stabilization of p53. Here we show that E7 stabilizes p53 in mouse embryo fibroblasts lacking p19(ARF). The stable p53 is active as a transcriptional activator, as evidenced by the increased expression of the p53-responsive mdm2 gene. Normally, MDM2 protein inhibits p53 function in an autoregulatory loop. Regulation of p53 by MDM2 is required for murine development as well as for proliferation of cultured human fibroblasts. However, E7-expressing human fibroblasts continue to divide even though E7 abrogates the ability of MDM2 and p53 to bind. Furthermore, E7-expressing cells are not more sensitive to UV light, an agent that has been reported to induce apoptosis mediated by p53. These results indicate that in addition to inhibiting the ability of MDM2 to regulate p53, E7 must block signaling steps downstream of p53 to allow cell division.
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PMID:The E7 oncoprotein of human papillomavirus type 16 stabilizes p53 through a mechanism independent of p19(ARF). 1043 49

Expression of Proteus mirabilis urease is governed by UreR, an AraC-like positive transcriptional activator. A poly(A) tract nucleotide sequence, consisting of A(6)TA(2)CA(2)TGGTA(5)GA(6)TGA(5), is located 16 bp upstream of the sigma(70)-like ureR promoter P2. Since poly(A) tracts of DNA serve as binding sites for the gene repressor histone-like nucleoid structuring protein (H-NS), we measured beta-galactosidase activity of wild-type Escherichia coli MC4100 (H-NS(+)) and its isogenic derivative ATM121 (hns::Tn10) (H-NS(-)) harboring a ureR-lacZ operon fusion plasmid (pLC9801). beta-Galactosidase activity in the H-NS(-) host strain was constitutive and sevenfold greater (P < 0.0001) than that in the H-NS(+) host. A recombinant plasmid containing cloned P. mirabilis hns was able to complement and restore repression of the ureR promoter in the H-NS(-) host when provided in trans. Deletion of the poly(A) tract nucleotide sequence from pLC9801 resulted in an increase in beta-galactosidase activity in the H-NS(+) host to nearly the same levels as that observed for wild-type pLC9801 harbored by the H-NS(-) host. Urease activity in strains harboring the recombinant plasmid pMID1010 (encoding the entire urease gene cluster of P. mirabilis) was equivalent in both the H-NS(-) background and the H-NS(+) background in the presence of urea but was eightfold greater (P = 0.0001) in the H-NS(-) background in the absence of urea. We conclude that H-NS represses ureR expression in the absence of urea induction.
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PMID:H-NS is a repressor of the Proteus mirabilis urease transcriptional activator gene ureR. 1076 73

The hydrolysis of urea by ureases of oral bacteria in dental plaque can cause a considerable increase in plaque pH, which can inhibit the development of dental caries. There is also indirect evidence that urea metabolism may promote the formation of calculus and that ammonia release from urea could exacerbate periodontal diseases. Actinomyces naeslundii, an early colonizer of the oral cavity and a numerically significant plaque constituent, demonstrates comparatively low levels of urease activity on isolation, so this organism has not been considered a major contributor to total oral urease activity. In this study it was observed that urease activity and urease-specific mRNA levels in A. naeslundii WVU45 can increase up to 50-fold during growth under nitrogen-limiting conditions. Using primer extension analysis, a putative, proximal, nitrogen-regulated promoter of the A. naeslundii urease gene cluster was identified. The functionality and nitrogen responsiveness of this promoter were confirmed using reporter gene fusions and 5' deletion analysis. The data indicated that regulation of urease expression by nitrogen availability in A. naeslundii may require a positive transcriptional activator. Plaque bacteria may experience nitrogen limitation when carbohydrates are present in excess. Therefore, based on the results of this study and in contrast to previous beliefs, strains of A. naeslundii may have the potential to be significant contributors to total plaque ureolysis, particularly during periods when there is an increased risk for caries development.
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PMID:Analysis of urease expression in Actinomyces naeslundii WVU45. 1108 80

The energy surface for the folding/unfolding reactions of the homodimeric coiled-coil peptide M2V GCN4-p1, a 33-residue segment comprising the leucine zipper domain of the transcriptional activator GCN4, was mapped by equilibrium and kinetic methods. Circular dichroism (CD) spectroscopy was used to monitor the urea-induced unfolding reaction at a series of temperatures and temperature-induced unfolding at a series of urea concentrations. A global analysis of the urea- and temperature-induced equilibrium unfolding data provides strong support for a two-state mechanism. The absence of a detectable population of intermediate states is also consistent with differential scanning calorimetry and thermal CD melts as a function of peptide concentration. Furthermore, a global analysis of stopped-flow CD kinetic data is consistent with a kinetic two-state mechanism as well. The urea dependence of the apparent folding and unfolding rate constants at a series of temperatures reveals that the activation enthalpy and entropy for unfolding in the absence of denaturant are both significantly greater than those for the refolding reaction. Although the unfolding barrier is dominated by the activation enthalpy, the activation entropy dominates the refolding barrier. The relative magnitudes of the urea dependence of the unfolding and refolding rate constants indicate that 55-65% of the surface area is buried in the transition state. The activation parameters imply a partially organized transition state and are consistent with a previous model in which the pair of C-terminal heptad repeats are docked in a coiled-coil-like motif [Zitzewitz et al. (2000) J. Mol. Biol. 296, 1105-1116].
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PMID:Mapping the energy surface for the folding reaction of the coiled-coil peptide GCN4-p1. 1117 Mar 89

The induction of phototropism in etiolated (dark-grown) seedlings exposed to an unidirectional pulse or extended irradiation with low fluence rate blue light (BL) requires the action of the phototropin (nph1) BL receptor. Although cryptochromes and phytochromes are not required for phototropic induction, these photoreceptors do modulate the magnitude of curvature resulting from phototropin activation. Modulatory increases in the magnitude of phototropic curvature have been termed "enhancement." Here, we show that phototropic enhancement is primarily a phytochrome A (phyA)-dependent red/far-red-reversible low fluence response. This phyA-dependent response is genetically separable from the basal phototropin-dependent response, as demonstrated by its retention under extended irradiation conditions in the nph4 mutant background, which normally lacks the basal BL-induced response. It is interesting that the nph4 mutants fail to exhibit the basal phototropin-dependent and phyA-dependent enhancement responses under limiting light conditions. Given that NPH4 encodes a transcriptional activator, auxin response factor 7 (ARF7), we hypothesize that the ultimate target(s) of phyA action during the phototropic enhancement response is a rate-limiting ARF-containing transcriptional complex in which the constituent ARFs can vary in identity or activity depending upon the irradiation condition.
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PMID:The enhancement of phototropin-induced phototropic curvature in Arabidopsis occurs via a photoreversible phytochrome A-dependent modulation of auxin responsiveness. 1140 10

Identification of the environmental triggers involved in the expression of virulence genes is a fundamental objective in studies of bacterial pathogens. For uropathogens, urea, found in the urinary tract at concentrations of up to 500 mm, functions as an environmental signal. Urea freely diffuses into the bacterium Providencia stuartii and activates UreR, a member of the AraC family of transcriptional activators. Active UreR promotes transcription of virulence-associated urease genes and alerts the organisms of its immediate milieu. Thus, the UreR.urea complex has a dual role, acting as both a transcriptional activator as well as an environmental sensor. Here, we describe the molecular events associated with activation of gene expression by urea-bound UreR. The K(d) of the urea.UreR binding reaction was measured as 0.2 mm by fluorescence quenching assays, and the shape of the binding curve indicated a single specific urea-binding site on UreR. Histidine residues are critical for urea binding in urease, and therefore to identify the urea-binding site in UreR, five mutant UreR forms were generated with histidine to alanine substitutions. Two of the mutants (UreR(c)) exhibited a constitutive phenotype by both activating transcription and binding to DNA with an increased affinity in the absence of urea. The UreR(c) bound urea with an affinity similar to that of wild-type UreR. We concluded, therefore, that the mutations resulting in constitutive activity were not involved in the UreR.urea interaction. UreR was activated, then, either by binding urea or by histidine to alanine substitutions at one of two positions. Circular dichroism indicated little change in the structure of UreR when activated, and size-exclusion chromatography demonstrated that both rUreR and rUreR(c) were dimers in both the presence and absence of urea. Thus, the structural changes associated with activation are subtle.
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PMID:Urea-dependent signal transduction by the virulence regulator UreR. 1214 87

Helicobacter pylori and Proteus mirabilis ureases are nickel-requiring metallo-enzymes that hydrolyse urea to NH3 and CO2. In both H. pylori and in an Escherichia coli model of H. pylori urease activity, a high affinity nickel transporter, NixA, is required for optimal urease activity, whereas the urea-dependent UreR positive transcriptional activator governs optimal urease expression in P. mirabilis. The H. pylori flbA gene is a flagellar biosynthesis and regulatory gene that modulates urease activity in the E. coli model of H. pylori urease activity. All flbA mutants of eight strains of H. pylori were non-motile and five had a strain-dependent alteration in urease activity. The flbA gene decreased urease activity 15-fold when expressed in E. coli containing the H. pylori urease locus and the nixA gene; this was reversed by disruption of flbA. The flbA gene decreased nixA transcription. flbA also decreased urease activity three-fold in E. coli containing the P. mirabilis urease locus in a urea- and UreR-dependent fashion. Here the flbA gene repressed the P. mirabilis urease promoter. Thus, FlbA decreased urease activity of both H. pylori and P. mirabilis, but through distinct mechanisms. H. pylori wild-type strain SS1 colonised gerbils at a mean of 5.4 x 10(6) cfu/g of antrum and caused chronic gastritis and lesions in the antrum. In contrast, the flbA mutant did not colonise five of six gerbils and caused no lesions, indicating that motility mediated by flbA was required for colonisation. Because FlbA regulates flagellar biosynthesis and secretion, as well as forming a structural component of the flagellar secretion apparatus, two seemingly unrelated virulence attributes, motility and urease, may be coupled in H. pylori and P. mirabilis and possibly also in other motile, ureolytic bacteria.
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PMID:The Helicobacter pylori flbA flagellar biosynthesis and regulatory gene is required for motility and virulence and modulates urease of H. pylori and Proteus mirabilis. 1244 80

The gas vesicle formation in Haloferax mediterranei occurs in the stationary growth phase and involves the 14 genes mc-gvpACNO and mc-gvpDEFGHIJKLM. The appearance of the two regulatory proteins GvpD and GvpE, and also of GvpF, was investigated during the growth of H. mediterranei. GvpD was only found during the stationary growth phase, GvpE was present from the late exponential to stationary growth phase, and GvpF was present only during the exponential growth, although the three genes were co-transcribed. The impact of GvpD and GvpE on the activity of the promoter of the mc-gvpACNO gene cluster encoding the gas vesicle structural proteins was analysed in H. volcanii transformants containing the mc-gvpA gene or a fusion of the mcA promoter with the bgaH reading frame encoding a halobacterial beta-galactosidase as reporter. The experiments proved that GvpE is a transcriptional activator, whereas GvpD is involved in the repression. Protein-protein affinity chromatography was used to search for putative binding partners of GvpD and GvpE. Both proteins were synthesized in Escherichia coli as his-tagged proteins, isolated under denaturing conditions and refolded by dialysis against buffers containing decreasing urea and increasing KCl concentrations up to 2.5 M. The Ni-NTA matrix tagged with GvpD-his or GvpE-his was incubated with soluble proteins of gas vesicle producing H. mediterranei cells. A 21 kDa protein was purified using the matrix tagged with GvpD-his which proved to be GvpE by Western analysis. Vice versa, GvpD was purified using the GvpE-his-Ni-NTA matrix. These results strongly suggested that GvpD and GvpE were able to interact and might constitute a regulatory system.
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PMID:Regulation of the expression of gas vesicle genes in Haloferax mediterranei: interaction of the two regulatory proteins GvpD and GvpE. 1286 59

Proteus mirabilis, a cause of catheter-associated urinary tract infection, relies on several virulence factors to colonize the urinary tract. Among these, urease contributes to the development of urinary stones resulting from the increase in local pH due to urease-mediated hydrolysis of urea to NH(3) and CO(2). UreR, an AraC-like transcriptional activator, activates transcription of the genes encoding the urease subunits and accessory proteins (ureDABCEFG) in the presence of urea. UreR also initiates transcription of its own gene in a urea-inducible manner by binding to the intergenic region between ureR and ureD. The intergenic region contains poly(A) tracts that appear to be the target of H-NS. It has been shown that Escherichia coli and P. mirabilis H-NS acts to repress transcription of ureR in an E. coli model system. It was hypothesized that H-NS represses urease gene expression in the absence of UreR and urea by binding to the intergenic region. To demonstrate this the P. mirabilis hns gene was cloned and the 15.6 kDa H-NS was overexpressed and purified as a myc-His tail fusion. Using a gel shift assay, purified H-NS-myc-His bound preferentially to a 609 bp DNA fragment containing the entire ureR-ureD intergenic region. H-NS and UreR were able to displace each other from the ureR-ureD intergenic region. Circular permutation analysis revealed that the intergenic region is bent. Moreover, H-NS recognizes this curvature, binds the DNA fragment and induces further bending of the DNA as shown by a circular ligation assay. The effects of H-NS, urea and temperature (25 vs 37 degrees C) on urease expression were shown in E. coli containing an hns knockout and P. mirabilis where expression was increased at 37 degrees C. Increased transcription from p(ureR) was seen in the E. coli hns knockout when temperature was increased from 25 to 37 degrees C. These findings suggest H-NS and UreR differentially regulate urease in a negative and positive manner, respectively.
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PMID:Differential regulation of the Proteus mirabilis urease gene cluster by UreR and H-NS. 1466 72

Double mutant cycle analysis was employed to ascertain the role of intra- and interchain salt-bridges in the folding and stability of the dimeric coiled-coil peptide, GCN4-p1, the 33-residue leucine zipper domain of the transcriptional activator GCN4. Equilibrium circular dichroism studies of the urea-induced unfolding reaction at neutral pH revealed that both types of ionic interactions, localized primarily in the N-terminal portion of the molecule, enhance the stability of the native coiled-coil. By contrast, comparable stopped-flow circular dichroism studies indicate that the salt-bridge interactions, with one possible exception, are not well formed in the transition state for folding. Although the E22Q/R25A double mutant failed to fold, fragmentation studies suggest that the E22/R25 intramolecular salt-bridge may play a critical role in stabilizing C-terminal nascent helices that drive the association reaction. The remaining salt-bridges appear to stabilize the parallel-stranded coiled-coil architecture of GCN4-p1 only after the peptide traverses the rate-limiting, dimeric transition state.
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PMID:Salt-bridges can stabilize but do not accelerate the folding of the homodimeric coiled-coil peptide GCN4-p1. 1503 63


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