Expression of VjbR under nutrient limitation conditions is regulated at the post-transcriptional level by specific acidic pH values and urocanic acid


Arocena, G.M.; <div class="autor_fcen" id="9341">Zorreguieta, A.</div>; Sieira, R.
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Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales
Biblioteca Digital (UBA-FCEN)
VjbR is a LuxR homolog that regulates transcription of many genes including important virulence determinants of the facultative intracellular pathogen Brucella abortus. This transcription factor belongs to a family of regulators that participate in a cell-cell communication process called quorum sensing, which enables bacteria to respond to changes in cell population density by monitoring concentration of self produced autoinducer molecules. Unlike almost all other LuxR-type proteins, VjbR binds to DNA and activates transcription in the absence of any autoinducer signal. To investigate the mechanisms by which Brucella induces VjbR-mediated transcriptional activation, and to determine how inappropriate spatio-temporal expression of the VjbR target genes is prevented, we focused on the study of expression of vjbR itself. By assaying different parameters related to the intracellular lifestyle of Brucella, we identified a restricted set of conditions that triggers VjbR protein expression. Such conditions required the convergence of two signals of different nature: a specific pH value of 5.5 and the presence of urocanic acid, a metabolite involved in the connection between virulence and metabolism of Brucella. In addition, we also observed an urocanic acid, pH-dependent expression of RibH2 and VirB7, two additional intracellular survival-related proteins of Brucella. Analysis of promoter activities and determination of mRNA levels demonstrated that the urocanic acid-dependent mechanisms that induced expression of VjbR, RibH2, and VirB7 act at the post-transcriptional level. Taken together, our findings support a model whereby Brucella induces VjbR-mediated transcription by modulating expression of VjbR in response to specific signals related to the changing environment encountered within the host. © 2012 Arocena et al.
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messenger RNA
RibH2 protein
transcription factor
unclassified drug
urocanic acid
VirB7 protein
VjbR protein
bacterial gene
bacterial metabolism
bacterial survival
bacterial virulence
controlled study
gene expression
intracellular bacterium
nutrient limitation
promoter region
protein expression
transcription initiation
transcription regulation
VjbR gene
Bacterial Proteins
Brucella abortus
Gene Expression Regulation, Bacterial
Glutamic Acid
Hydrogen-Ion Concentration
Quorum Sensing
Transcription Factors
Urocanic Acid
Brucella melitensis biovar Abortus