Mechanism of strand exchange from RecA-DNA synaptic and D-loop structures

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Homologous recombination is a fundamental DNA repair process.
• RecA family ATPases are essential catalysts, forming filaments with DNA and ATP.
• The mechanism of RecA-mediated strand exchange and homology search remains incompletely understood.

Purpose of the Study:

• To elucidate the structural mechanisms of RecA synaptic filament formation and function.
• To understand how RecA searches for homology and catalyzes strand exchange.
• To provide mechanistic insights into the D-loop formation during homologous recombination.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to analyze RecA synaptic mini-filaments.
• Structures of RecA-D-loop complexes with varying heteroduplex lengths were determined.
• Biophysical and biochemical analyses were employed to study DNA binding and strand exchange.

Main Results:

• The C-terminal domain of RecA facilitates dsDNA binding and opening.
• RecA's L2 loop inserts into dsDNA, propagating duplex opening.
• Homology recognition enhances dsDNA opening by stabilizing interactions at a secondary DNA-binding site.
• A probabilistic mechanism limits sampling length and allows for multiple synapses.

Conclusions:

• RecA utilizes a dynamic mechanism involving dsDNA opening and homology-dependent stabilization.
• This mechanism allows efficient sampling of homologous sequences on donor DNA.
• The findings provide crucial mechanistic insights into the fundamental process of homologous recombination.