A bend, flip and trap mechanism for transposon integration

Area of Science:

• Molecular Biology
• Structural Biology
• Genomics

Background:

• Cut-and-paste DNA transposons, particularly the mariner/Tc1 family, are valuable for genome engineering.
• These transposons exhibit specific insertion at TA target sites.

Purpose of the Study:

• To elucidate the structural mechanism of mariner/Tc1 transposase-mediated DNA integration.
• To understand the molecular basis for TA target site selection by the Mos1 transposase.

Main Methods:

• X-ray crystallography of the Mos1 transposase complexed with transposon ends and target DNA.
• Fluorescence spectroscopy to study dynamic base flipping in solution.
• In vitro transposition assays to assess the role of specific transposase residues.

Main Results:

• The crystal structure revealed significant distortion of target DNA and flipping of adenine bases into extra-helical positions post-integration.
• Fluorescence experiments confirmed dynamic adenine base flipping.
• Specific transposase residues (W159, R186, F187, K190) were identified as crucial for stabilizing DNA distortions and facilitating transposition.
• Base-specific interactions between the transposase and flipped adenine backbone atoms were observed, explaining TA target selection.

Conclusions:

• The study provides a detailed structural insight into the DNA integration mechanism of mariner/Tc1 transposases.
• The findings offer a molecular explanation for TA target site specificity.
• This knowledge can guide the rational redesign of mariner/Tc1 transposases for altered target specificities in genome engineering applications.