Transposition into replicating DNA occurs through interaction with the processivity factor.

The bacterial transposon Tn7 directs transposition into actively replicating DNA by a mechanism involving the transposon-encoded protein TnsE. Here we show that TnsE physically and functionally interacts with the processivity factor of the DNA replication machinery in vivo and in vitro. Our work establishes an in vitro TnsABC+E transposition reaction reconstituted from purified proteins and target DNA structures. Using the in vitro reaction we confirm that the processivity factor specifically reorders TnsE-mediated transposition events on target DNAs in a way that matches the bias with active DNA replication in vivo. The TnsE interaction with an essential and conserved component of the replication machinery, and a DNA structure reveals a mechanism by which Tn7, and probably other elements, selects target sites associated with DNA replication.