The multiple stress responsive transcriptional regulator Rv3334 ofMycobacterium tuberculosisis an autorepressor and a positive regulator ofkstR

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Rv3334 protein of Mycobacterium tuberculosis belongs to the MerR family of transcriptional regulators and is upregulated during hypoxia and other stress conditions. Employing GFP reporter constructs, mobility shift assays and ChIP assays, we demonstrate that Rv3334 binds to its own promoter and acts as an autorepressor. We were able to locate a 22 bp palindrome in its promoter that we show to be the cognate binding sequence of Rv3334. Using chase experiments, we could conclusively prove the requirement of this palindrome for Rv3334 binding. Recombinant Rv3334 readily formed homodimers in vitro, which could be necessary for its transcriptional regulatory role in vivo. Although the DNA-binding activity of the protein was abrogated by the presence of certain divalent metal cations, the homodimer formation remained unaffected. In silico predictions and subsequent assays using GFP reporter constructs and mobility shift assays revealed that the expression of ketosteroid regulator gene (kstR), involved in lipid catabolism, is positively regulated by Rv3334. ChIP assays with aerobically grown M. tuberculosis as well as dormant bacteria unambiguously prove that Rv3334 specifically upregulates expression of kstR during dormancy. Our study throws light on the possible role of Rv3334 as a master regulator of lipid catabolism during hypoxia-induced dormancy.

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