| Summary: | The protein MucR from <i>Brucella abortus</i> has been described as a transcriptional regulator of many virulence genes. It is a member of the Ros/MucR family comprising proteins that control the expression of genes important for the successful interaction of α-proteobacteria with their eukaryotic hosts. Despite clear evidence of the role of MucR in repressing virulence genes, no study has been carried out so far demonstrating the direct interaction of this protein with the promoter of its target gene <i>babR</i> encoding a LuxR-like regulator repressing <i>virB</i> genes. In this study, we show for the first time the ability of MucR to bind the promoter of <i>babR</i> in electrophoretic mobility shift assays demonstrating a direct role of MucR in repressing this gene. Furthermore, we demonstrate that MucR can bind the <i>virB</i> gene promoter. Analyses by RT-qPCR showed no significant differences in the expression level of <i>virB</i> genes in <i>Brucella abortus</i> CC092 lacking MucR compared to the wild-type <i>Brucella abortus</i> strain, indicating that MucR binding to the <i>virB</i> promoter has little impact on <i>virB</i> gene expression in <i>B. abortus</i> 2308. The MucR modality to bind the two promoters analyzed supports our previous hypothesis that this is a histone-like protein never found before in <i>Brucella</i>.
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