In order to further confirm our finding that TcaR forms complex with viral ssDNA, the M13 and wX174 phage ssDNA circles were used as probes in EMSA to evaluate TcaR binding. As shown in Figure 4A , TcaR reduced the mobility of the M13 and wX174 ssDNA, but S. epidermidis IcaR and S. aureus MarR family protein SAR2349 had no specific interactions with ssDNA. This indicated that TcaR has strong viral ssDNA-binding ability. It is also worth noting that other MarR family protein and TetR family protein do not have such ssDNA binding properties with high affinity, suggesting that the results from TcaR studies are not an artifact due to simple charge interactions between TcaR and ssDNA. Furthermore, since the attempt to obtain the TcaR-ssDNA complex structure was not successful, we resorted to EM analysis to image TcaR-wx174 complex and to pursue its 3-D reconstruction. After staining for 4 min with 2.5% uranyl acetate, EM analysis was performed with a Tecnai tm G 2 Spirit Bio TWIN (FEI CO., The Netherlands) using 120kV acceleration voltage. As seen in Figure 4B -D, EM imaging revealed that no complex was found in the negative control sections, whereas TcaR form a nucleoprotein filament with a circular viral wX174-ssDNA fully covered with proteins, suggesting strong and cooperatively interaction between viral ssDNA and TcaR. This is consistent with the EMSA results we observed. We are now testing another EM method as described by Lurz R et al. [28] to confirm the cooperative binding between the TcaR and viral wX174-ssDNA.