Binding of the protein from Thermus aquaticus ISLtaq1 to its inverted repeat in vitro

We have isolated from Thermus aquaticus an insertion-sequence-like genetic element (ISLtaq1) that induces thermotolerance and has a high sequence similarity to IS150 belonging to the IS3 family. An open reading frame on ISLtaq1, termed ORF1, encodes the ORF1 protein, which carries a DNA-binding motif. In this study, we found an imperfect inverted repeat in ISLtaq1. We next overproduced and purified a His-tagged ORF1 protein. Gel retardation analysis demonstrated that this protein specifically bound to an DNA fragment containing the inverted repeat in ISLtaq1. These results suggest that ISLtaq1 and the ORF1 protein are an insertion sequence and part of the transposase encoded by ISLtaq1, respectively.