Structural mechanism of bridge RNA-guided recombination

Area of Science:

• Molecular Biology
• Genomics
• Structural Biology

Background:

• Insertion sequence (IS) elements are prokaryotic transposable elements.
• IS110 family elements utilize a recombinase and a bridge RNA (bRNA) for DNA transposition.
• The bRNA confers modular specificity to target and donor DNA via two programmable loops.

Purpose of the Study:

• To elucidate the structural mechanism of IS110 recombinase-mediated DNA recombination.
• To visualize the IS110 synaptic complex at different stages of the reaction cycle using cryo-electron microscopy.
• To understand how the bRNA confers specificity to DNA binding and cleavage.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structures of the IS110 recombinase.
• Structures were captured in complex with bRNA, target DNA, and donor DNA at three distinct reaction stages.
• Comparative analysis of the structures revealed the dynamic process of recombination.

Main Results:

• The IS110 synaptic complex consists of two recombinase dimers, each interacting with a specific bRNA loop and DNA.
• A composite RuvC-Tnp active site formed across the dimers facilitates DNA cleavage and strand exchange.
• The study identified three key steps: 5'-phosphoserine intermediate formation, Holliday junction formation, and resolution.

Conclusions:

• The bispecific RNA (bRNA) is crucial for directing IS110 recombinase to specific target and donor DNA sequences.
• The structural data reveals a novel mechanism for programmable DNA recombination mediated by RNA-protein-DNA interactions.
• This work provides atomic-level insights into the transposition process of IS elements.