Tn7 recognizes transposition target structures associated with DNA replication using the DNA-binding protein TnsE

We report that the bacterial transposon Tn7 selects targets by recognizing features associated with DNA replication using the transposon-encoded DNA-b inding protein TnsE. We show that Tn7 transposition directed by TnsE occurs in one orientation with respect to chromosomal DNA replication, indicating that a structure or complex involved in DNA replication is likely to be a critical determinant of TnsE insertion. We find that mutant TnsE proteins t hat allow higher levels of transposition also bind DNA better than the wild -type protein. The increased binding affinity displayed by the TnsE high-ac tivity mutants indicates that DNA binding is relevant to transposition acti vity and suggests that TnsE interacts directly with target DNAs. In vitro, TnsE interacts preferentially with certain DNA structures, indicating a mec hanism for the TnsE-mediated orientation and insertion preference. The patt ern of TnsE-mediated insertion events around the Escherichia coli chromosom e provides insight into how DNA replication forks proceed in vivo.