Structural basis for DNA targeting by the Tn7 transposon.

Area of Science:

• Molecular Biology
• Genetics
• Structural Biology

Background:

• Tn7 transposable elements exhibit remarkable target-site specificity.
• The TnsC protein is crucial for coordinating target selection and transpososome assembly.
• TnsC acts as a regulatory hub, preventing multiple insertions at the same site.

Purpose of the Study:

• To elucidate the high-resolution structure of TnsC bound to its target DNA.
• To understand the mechanism of target-site selection and regulation by TnsC.
• To reveal how Tn7 elements ensure precise spacing between target and integration sites.

Main Methods:

• High-resolution cryo-electron microscopy (cryo-EM).
• Utilized a gain-of-function TnsC variant and a specific DNA substrate.
• Reconstituted target DNA recruitment and transpososome assembly intermediates.

Main Results:

• Determined the cryo-EM structure of TnsC forming an asymmetric ring on target DNA.
• TnsC segregates target-site selection and paired-end complex interaction to different faces of the ring.
• TnsC recognizes pre-distorted DNA, using distortion for site finding but not DNA remodeling for transposition activation.

Conclusions:

• TnsC's asymmetric ring structure dictates target selection and integration site spacing.
• ATP hydrolysis by TnsC regulates ring stability, preventing insertions near existing elements.
• This mechanism ensures precise and regulated transposition by Tn7 elements.