Strong TcaR Binding to ssDNA Oligomers Revealed by EMSA TcaR is known to bind and regulate the ica promoter [4] . We previously identified that TcaR most strongly interacts with IcaR DNA1 (a 33-mer pseudo-palindromic sequence containing consensus sequence TTNNAA) compared with other designed IcaR DNA fragments [17] . However, when using the sense strand of IcaR DNA1 (IcaR DNA1S) and the antisense strand of IcaR DNA1 (IcaR DNA1A) ( Figure 1A ) as controls in electrophoretic mobility shift assays (EMSA), the result demonstrated that TcaR shows a stronger preferences toward ssDNA fragments (IcaR DNA1S and DNA1A) ( Figure 1B) . To determine the type and length of the TcaR-binding site on ssDNA, a series of GC-rich and AT-rich ssDNA segments were designed ( Figure 1A ) [20, 21] . Their TcaR binding ability was tested using EMSA. As shown in Figure 1C , TcaR does not significantly interact with 17-mer GCrich (GC17) and AT-rich (AT17) ssDNA oligomers, but shows strong interaction with 33-mer GC-rich (GC33) and AT-rich (AT33) ssDNA sequences with a preference toward the 33-mer ssDNA sequence with a molar ratio of 1:1. Thus, we suggest that TcaR prefers binding to the 33-mer ssDNA.