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

Conjugation of the Agrobacterium Ti plasmid pTiC58 is regulated by a hierarchy involving induction by the opines agrocinopines A and B and a quorum-sensing system. Regulation by the opines is mediated by the repressor AccR, while quorum sensing is effected by the transcriptional activator TraR and its ligand, the acyl-homoserine lactone signal molecule Agrobacterium autoinducer (AAI). These last two elements combine to activate expression of the tra system at high population densities. Sequence analysis indicated that traR is the fourth gene of an operon, which we named arc, that is transcribed divergently from accR. Complementation analysis of mutations in the genes 5' to traR showed that the other members of the arc operon are not required for conjugation. Analysis of lacZ reporter fusions demonstrated that traR expression is regulated directly by AccR. Deletion analysis showed that AccR-regulated expression of traR initiates from a promoter located in the intergenic region between accR and orfA, the first gene of the arc operon. Reverse transcriptase-polymerase chain reaction (RT-PCR) and primer extension analyses indicated that the arc transcript initiates upstream of orfA and proceeds uninterrupted through traR. These results are consistent with a model in which quorum sensing is subordinate to the opine regulon because traR has become associated with an operon controlled by the opine-responsive transcriptional regulator.
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PMID:Hierarchical gene regulatory systems arising from fortuitous gene associations: controlling quorum sensing by the opine regulon in Agrobacterium. 1036 9

Carbapenems are potent beta-lactam antibiotics with a broad spectrum of activity against both Gram positive and Gram negative bacteria. As naturally produced metabolites, they have been isolated from species of Streptomyces, Erwinia and Serratia. The latter two members of the Enterobacteriaceae have proved to be genetically amenable and a growing body of research on these organisms now exists concerning the genes responsible for carbapenem biosynthesis and the regulatory mechanisms controlling their expression. A cluster of nine carbapenem (car) genes has been identified on the chromosome of Erwinia carotovora. These genes encode the enzymes required for construction of carbapenem and the proteins responsible for a novel beta-lactam resistance mechanism, conferring carbapenem immunity in the producing host. Although sharing no homology with the well known enzymes of penicillin biosynthesis, two of the encoded proteins are apparently similar to enzymes of the clavulanic acid biosynthetic pathway implying a common mechanism for construction of the beta-lactam ring. In addition, a transcriptional activator is encoded as the first gene of the carbapenem cluster and this allows positive expression of the remaining downstream genes in response to a quorum sensing, N-acyl homoserine lactone, signalling molecule.
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PMID:Molecular genetics of carbapenem antibiotic biosynthesis. 1042 86

Numerous species of bacteria use an elegant regulatory mechanism known as quorum sensing to control the expression of specific genes in a cell-density dependent manner. In Gram-negative bacteria, quorum sensing systems function through a cell-to-cell signal molecule (autoinducer) that consists of a homoserine lactone with a fatty acid side chain. Such is the case in the opportunistic human pathogen Pseudomonas aeruginosa, which contains two quorum sensing systems (las and rhl) that operate via the autoinducers, N-(3-oxododecanoyl)-L-homoserine lactone and N-butyryl-L-homoserine lactone. The study of these signal molecules has shown that they bind to and activate transcriptional activator proteins that specifically induce numerous P. aeruginosa virulence genes. We report here that P. aeruginosa produces another signal molecule, 2-heptyl-3-hydroxy-4-quinolone, which has been designated as the Pseudomonas quinolone signal. It was found that this unique cell-to-cell signal controlled the expression of lasB, which encodes for the major virulence factor, LasB elastase. We also show that the synthesis and bioactivity of Pseudomonas quinolone signal were mediated by the P. aeruginosa las and rhl quorum sensing systems, respectively. The demonstration that 2-heptyl-3-hydroxy-4-quinolone can function as an intercellular signal sheds light on the role of secondary metabolites and shows that P. aeruginosa cell-to-cell signaling is not restricted to acyl-homoserine lactones.
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PMID:Quinolone signaling in the cell-to-cell communication system of Pseudomonas aeruginosa. 1065 66

Conjugal transfer of the Ti plasmid pTiC58 is regulated by a quorum-sensing system involving the transcriptional activator TraR and the acyl homoserine lactone autoinducer N-(3-oxo-octanoyl)-L-homoserine lactone (AAI). Activation of tra gene expression by TraR and AAI is inhibited by TraM, an 11 kDa protein also coded for by the Ti plasmid. Previous studies suggested that TraM interferes with TraR activity by directly interacting with the activator protein. Using the yeast two-hybrid system, constructs of Saccharomyces cerevisiae containing a fusion of traR to the B42 domain of the prey plasmid pJG4.5 and a fusion of traM to the lexA gene of the bait plasmid pEG202 produced beta-galactosidase and grew on medium lacking leucine, both phenotypes indicative of an interaction between the two proteins. Early termination mutants and substitution mutants mapping to the C-terminus of TraM were isolated by screening for alleles unable to interfere with TraR activity in Agrobacterium tumefaciens. These mutants all failed to interact with the TraR fusion in the two-hybrid system. An N-terminal deletion mutant of TraM lacking the first 27 residues weakly interacted with TraR in the two-hybrid system whereas deletions of 48 amino acids or more abolished the interaction. As assessed by Western blot analysis, the mutant fusion proteins were produced at levels indistinguishable from that of the wild-type TraM in the yeast tester strain. Mutants of TraR that were not inhibited by TraM in A. tumefaciens were isolated and fell into two classes. In the first, the mutation resulted in increased expression of wild-type TraR. In the second, a proline residue at position 176 was changed to serine (P176 --> S) or to leucine (P176 --> L). The P176 --> S mutant interacted with wild-type TraM, but at a detectably lower level, in the two-hybrid assay. Mutants of TraR with N-terminal deletions as large as 105 amino acids interfered with the ability of TraM to inhibit wild-type TraR in A. tumefaciens. Two-hybrid assays indicated that these mutants, as well as a C-terminal 49 residue fragment of TraR, can interact with TraM. We conclude that TraM and TraR interact in vivo and that this interaction is responsible for inhibition of TraR-mediated activation. We also conclude that the two proteins interact with each other through domains located at their respective C-termini.
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PMID:Modulating quorum sensing by antiactivation: TraM interacts with TraR to inhibit activation of Ti plasmid conjugal transfer genes. 1056 72

Quorum sensing (QS) governs the production of virulence factors and the architecture and sodium dodecyl sulphate (SDS) resistance of biofilm-grown Pseudomonas aeruginosa. P. aeruginosa QS requires two transcriptional activator proteins known as LasR and RhlR and their cognate autoinducers PAI-1 (N-(3-oxododecanoyl)-L-homoserine lactone) and PAI-2 (N-butyryl-L-homoserine lactone) respectively. This study provides evidence of QS control of genes essential for relieving oxidative stress. Mutants devoid of one or both autoinducers were more sensitive to hydrogen peroxide and phenazine methosulphate, and some PAI mutant strains also demonstrated decreased expression of two superoxide dismutases (SODs), Mn-SOD and Fe-SOD, and the major catalase, KatA. The expression of sodA (encoding Mn-SOD) was particularly dependent on PAI-1, whereas the influence of autoinducers on Fe-SOD and KatA levels was also apparent but not to the degree observed with Mn-SOD. beta-Galactosidase reporter fusion results were in agreement with these findings. Also, the addition of both PAIs to suspensions of the PAI-1/2-deficient double mutant partially restored KatA activity, while the addition of PAI-1 only was sufficient for full restoration of Mn-SOD activity. In biofilm studies, catalase activity in wild-type bacteria was significantly reduced relative to planktonic bacteria; catalase activity in the PAI mutants was reduced even further and consistent with relative differences observed between each strain grown planktonically. While wild-type and mutant biofilms contained less catalase activity, they were more resistant to hydrogen peroxide treatment than their respective planktonic counterparts. Also, while catalase was implicated as an important factor in biofilm resistance to hydrogen peroxide insult, other unknown factors seemed potentially important, as PAI mutant biofilm sensitivity appeared not to be incrementally correlated to catalase levels.
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PMID:Quorum sensing in Pseudomonas aeruginosa controls expression of catalase and superoxide dismutase genes and mediates biofilm susceptibility to hydrogen peroxide. 1059 32

The Vibrio fischeri luminescence (lux) operon is regulated by a quorum-sensing system that involves the transcriptional activator (LuxR) and an acyl-homoserine lactone signal. Transcriptional activation requires the presence of a 20-base inverted repeat termed the lux box at a position centered 42.5 bases upstream of the transcriptional start of the lux operon. LuxR has proven difficult to study in vitro. A truncated form of LuxR has been purified, and together with sigma(70) RNA polymerase it can activate transcription of the lux operon. Both the truncated LuxR and RNA polymerase are required for binding to lux regulatory DNA in vitro. We have constructed an artificial lacZ promoter with the lux box positioned between and partially overlapping the consensus -35 and -10 hexamers of an RNA polymerase binding site. LuxR functioned as an acyl-homoserine lactone-dependent repressor at this promoter in recombinant Escherichia coli. Furthermore, multiple lux boxes on an independent replicon reduced the repressor activity of LuxR. Thus, it appears that LuxR can bind to lux boxes independently of RNA polymerase binding to the promoter region. A variety of LuxR mutant proteins were studied, and with one exception there was a correlation between function as a repressor of the artificial promoter and activation of a native lux operon. The exception was the truncated protein that had been purified and studied in vitro. This protein functioned as an activator but not as a repressor in E. coli. The data indicate that the mutual dependence of purified, truncated LuxR and RNA polymerase on each other for binding to the lux promoter is a feature specific to the truncated LuxR and that full-length LuxR by itself can bind to lux box-containing DNA.
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PMID:Conversion of the Vibrio fischeri transcriptional activator, LuxR, to a repressor. 1063 17

Conjugal transfer of the Ti plasmids from Agrobacterium tumefaciens is controlled by autoinduction via the transcriptional activator TraR and the acyl-homoserine lactone ligand, Agrobacterium autoinducer (AAI). This control process is itself regulated by opines, which are small carbon compounds produced by the crown gall tumors that are induced by the bacteria. Opines control autoinduction by regulating the expression of traR. Transfer of pTiC58 from donors grown with agrocinopines A and B, the conjugal opines for this Ti plasmid, was detected only after the donors had reached a population level of 10(7) cells per cm(2). Donors incubated with the opines and AAI transferred their Ti plasmids at population levels about 10-fold lower than those incubated with opines only. Transcription of the tra regulon, as assessed by monitoring a traA::lacZ reporter, showed a similar dependence on the density of the donor population. However, even in cultures at low population densities that were induced with opines and AAI, there was a temporal lag of between 15 and 20 h in the development of conjugal competence. Moreover, even after this latent period, maximal transfer frequencies required several hours to develop. This lag period was independent of the population density of the donors but could be reduced somewhat by addition of exogenous AAI. Quorum-dependent development of conjugal competence required control by the opine regulon; donors harboring a mutant of pTiC58 deleted for the master opine responsive repressor accR transferred the Ti plasmid at maximum frequencies at very low population densities. Similarly, an otherwise wild-type derivative of pTiC58 lacking traM, which codes for an antiactivator that inhibits TraR activity, transferred at high frequency in a population-independent manner in the absence of the conjugal opines. Thus, while quorum sensing is dependent upon autoinduction, the two phenomena are not synonymous. We conclude that conjugal transfer of pTiC58 is regulated in a quorum-dependent fashion but that supercontrol of the TraR-AAI system by opines and by TraM results in a complex control process that requires not only the accumulation of AAI but also the expression of TraR and the synthesis of this protein at levels that overcome the inhibitory activity of TraM.
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PMID:Quorum sensing but not autoinduction of Ti plasmid conjugal transfer requires control by the opine regulon and the antiactivator TraM. 1064 35

Conjugal transfer of Agrobacterium tumefaciens Ti plasmids is regulated by quorum sensing via the transcriptional activator TraR and the acyl-homoserine lactone Agrobacterium autoinducer (AAI). Unique to this system, the activity of TraR is negatively modulated by an antiactivator called TraM. Analyses from yeast two-hybrid studies suggest that TraM directly interacts with the activator, but the conditions under which these components interact and the region of TraR responsible for this interaction are not known. Induction of traM in a strain in which TraR was activating transcription of a reporter system led to rapid cessation of gene expression. As assessed by a genetic assay that measures AAI-dependent DNA binding, TraM inhibited TraR function before and after the transcription factor had bound to its DNA recognition site. Consistent with this observation, in gel retardation assays, purified TraM abolished the DNA binding activity of TraR in a concentration-dependent manner. Such inhibition occurred independent of the order of addition of the reactants. As assessed by far Western analyses TraM interacts with TraR by directly binding the activator. TraM in its native form interacted with native TraR and also with heat-treated TraR but only when SDS was included with the denatured protein. TraM interacted with TraR on blots prepared with total lysates of cells grown in the presence and absence of AAI. Far Western analysis of N- and C-terminal deletion mutants localized a domain of TraR contributing to TraM binding to the C-terminal portion of the activator protein. Random mutagenesis by hydroxylamine treatment and error-prone polymerase chain reaction identified several residues in this region of TraR important for interacting with TraM as well as for transcriptional activation or/and DNA binding. We conclude that TraM inhibits TraR by binding to the activator at a domain within or close to the helix-turn-helix motif located at the C terminus of the protein.
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PMID:The antiactivator TraM interferes with the autoinducer-dependent binding of TraR to DNA by interacting with the C-terminal region of the quorum-sensing activator. 1071 83

The luminescence (lux) operon (luxICDABEG) of the symbiotic bacterium Vibrio fischeri is regulated by the transcriptional activator LuxR and two acyl-homoserine lactone (acyl-HSL) autoinducers (the luxI-dependent 3-oxo-hexanoyl-HSL [3-oxo-C6-HSL] and the ainS-dependent octanoyl-HSL [C8-HSL]) in a population density-responsive manner called quorum sensing. To identify quorum-sensing-regulated (QSR) proteins different from those encoded by lux genes, we examined the protein patterns of V. fischeri quorum-sensing mutants defective in luxI, ainS, and luxR by two-dimensional polyacrylamide gel electrophoresis. Five non-Lux QSR proteins, QsrP, RibB, AcfA, QsrV, and QSR 7, were identified; their production occurred preferentially at high population density, required both LuxR and 3-oxo-C6-HSL, and was inhibited by C8-HSL at low population density. The genes encoding two of the QSR proteins were characterized: qsrP directs cells to synthesize an apparently novel periplasmic protein, and ribB is a homolog of the Escherichia coli gene for 3,4-dihydroxy-2-butanone 4-phosphate synthase, a key enzyme for riboflavin synthesis. The qsrP and ribB promoter regions each contained a sequence similar to the lux operon lux box, a 20-bp region of dyad symmetry necessary for LuxR/3-oxo-C6-HSL-dependent activation of lux operon transcription. V. fischeri qsrP and ribB mutants exhibited no distinct phenotype in culture. However, a qsrP mutant, in competition with its parent strain, was less successful in colonizing Euprymna scolopes, the symbiotic host of V. fischeri. The newly identified QSR genes, together with the lux operon, define a LuxR/acyl-HSL-responsive quorum-sensing regulon in V. fischeri.
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PMID:LuxR- and acyl-homoserine-lactone-controlled non-lux genes define a quorum-sensing regulon in Vibrio fischeri. 1078 50

Luminescence in Vibrio fischeri is controlled by a population density-responsive regulatory mechanism called quorum sensing. Elements of the mechanism include: LuxI, an acyl-homoserine lactone (acyl-HSL) synthase that directs synthesis of the diffusible signal molecule, 3-oxo-hexanoyl-HSL (V. fischeri autoinducer-1, VAI-1); LuxR, a transcriptional activator protein necessary for response to VAI-1; GroEL, which is necessary for production of active LuxR; and AinS, an acyl-HSL synthase that catalyzes the synthesis of octanoyl-HSL (VAI-2). The population density-dependent accumulation of VAI-1 triggers induction of lux operon (luxICDABEG; genes for luminescence enzymes and for LuxI) transcription and luminescence by binding to LuxR, forming a complex that facilitates the association of RNA polymerase with the luxoperon promoter. VAI-2, which apparently interferes with VAI-1 binding to LuxR, operates to limit premature luxoperon induction. Hierarchical control is imposed on the system by 3':5'-cyclic AMP (cAMP) and cAMP receptor protein (CRP), which are necessary for activated expression of luxR. Several non-lux genes in V. fischeri are controlled by LuxR and VAI-1. Quorum regulation in V. fischeri serves as a model for LuxI/LuxR-type quorum sensing systems in other gram-negative bacteria.
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PMID:Quorum regulation of luminescence in Vibrio fischeri. 1094 79


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