Target DNA structure plays a critical role in Tn7 transposition

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Abstract
The bacterial transposon Tn 7 utilizes four Tn 7 ‐encoded proteins, TnsA, TnsB, TnsC and TnsD, to make insertions at a specific site termed att Tn 7 . This target is selected by the binding of TnsD to att Tn 7 in a sequence‐specific manner, followed by the binding of TnsC and activation of the transposase. We show that TnsD binding to att Tn 7 induces a distortion at the 5′ end of the binding site and TnsC contacts the region of att Tn 7 distorted by TnsD. Previous work has shown that a target site containing triplex DNA, instead of TnsD– att Tn 7 , can recruit TnsABC and effect site‐ specific insertion of Tn 7 . We propose that the DNA distortion imposed by TnsD on att Tn 7 , like the altered DNA structure via triplex formation, serves as a signal to recruit TnsC. We also show that TnsD primarily contacts the major groove of DNA, whereas TnsC is a minor groove binding protein. The footprint of the TnsC–TnsD– att Tn 7 nucleoprotein complex includes and extends beyond the Tn 7 insertion site, where TnsC forms a platform to receive and activate the transposase to carry out recombination.