DNA sequence alignment by microhomology sampling during homologous recombination

Area of Science:

• Molecular Biology
• Genetics
• Biophysics

Background:

• Homologous recombination (HR) is essential for genetic information exchange.
• RecA/Rad51 recombinases search extensive DNA sequences to find homologous targets.
• Understanding the mechanism of DNA pairing by Rad51 is crucial.

Purpose of the Study:

• To visualize the real-time DNA pairing and alignment process mediated by Rad51.
• To elucidate the search mechanism employed by Rad51 for homologous DNA sequences.

Main Methods:

• Single-molecule imaging techniques were utilized.
• Real-time observation of Rad51 activity on DNA substrates.

Main Results:

• Rad51 employs a length-based recognition mechanism to interrogate double-strand DNA (dsDNA).
• Kinetically selective identification of 8-nucleotide (nt) microhomology tracts guides the search.
• Strand exchange proceeds in precise 3-nt steps, correlating with DNA triplet organization.

Conclusions:

• Rad51's search mechanism efficiently identifies homologous DNA targets through kinetic selection.
• The findings reveal the physical basis of DNA recombination and its evolutionary significance.
• This study provides critical insights into the step-wise progression of DNA strand exchange.