![]() ![]() Binding of FrrA was also affected by the addition of genistein. The replacement of several nucleotides or the insertion of additional spacer nucleotides prevented binding. The protein, which was heterologously expressed and purified from Escherichia coli, binds to two palindrome-like DNA elements (operator A and operator B), which are located in the intergenic region between freC and frrA. We identified the correct translational start codon of frrA and showed that the gene is inducible by genistein and daidzein. A deletion of frrA leads to increased expression of freB in the absence of an inducer. Upstream of freCAB and in the opposite orientation, FrrA (systematic designation Blr4322), which has similarity to TetR-type regulators, is encoded. This includes the three genes freC, freA, and freB (systematic designations bll4319, bll4320, and bll4321), which are likely to form a genistein-, daidzein-, and coumestrol-inducible operon and to encode a multidrug efflux system. Previous microarray analyses revealed that in Bradyrhizobium japonicum, about 100 genes are induced by genistein, an isoflavonoid secreted by soybean. ![]()
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