To clarify whether the ssDNA binding site of TcaR is close, or identical, to the dsDNA binding site, a TcaR quadruple mutant (4 positively charged amino acids responsible for DNA binding mutated to alanines to produce R71A/K73A/R93A/K95A) [17] was designed and its ssDNA and dsDNA binding ability tested. As seen in Figure 1H , the mutant failed to interact with either dsDNA or ssDNA. This indicated that these amino acids are essential for binding in both ssDNA and dsDNA.