Target DNA structure plays a critical role in Tn7 transposition

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• The bacterial transposon Tn7 mediates site-specific DNA integration using four proteins: TnsA, TnsB, TnsC, and TnsD.
• Target site selection is primarily mediated by the TnsD protein binding to the attTn7 DNA sequence.

Purpose of the Study:

• To elucidate the molecular mechanisms by which TnsD and TnsC interact with the attTn7 target site.
• To understand how DNA distortion influences the recruitment and activation of the Tn7 transposition machinery.

Main Methods:

• DNA-protein binding assays to determine interaction sites and grooves.
• Analysis of DNA structural changes induced by protein binding.
• Comparison of TnsD-attTn7 interactions with triplex DNA-mediated recruitment.

Main Results:

• TnsD binding to attTn7 induces significant DNA distortion at the 5' end of the binding site.
• TnsC interacts with the distorted DNA region and binds to the minor groove, while TnsD binds the major groove.
• The TnsC-TnsD-attTn7 complex footprint encompasses the insertion site, with TnsC acting as a platform for transposase activation.

Conclusions:

• DNA distortion at attTn7, induced by TnsD, acts as a crucial signal for TnsC recruitment.
• The distinct DNA groove binding preferences of TnsD and TnsC are essential for precise target site recognition and transposition.
• TnsC plays a central role in assembling and activating the Tn7 transposase complex at the specific attTn7 site.