recA protein promoted DNA strand exchange

Area of Science:

• Molecular Biology
• Biochemistry
• DNA Repair Mechanisms

Background:

• RecA protein is essential for homologous recombination and DNA repair.
• Single-stranded DNA binding protein (SSB) plays a regulatory role in DNA metabolic processes.

Purpose of the Study:

• To physically characterize the complexes formed by RecA protein, single-stranded DNA (ssDNA), and SSB protein.
• To elucidate the role of SSB in RecA-mediated DNA strand exchange.

Main Methods:

• Biochemical assays to study protein-DNA complex formation.
• Analysis of RecA protein binding stoichiometry to ssDNA in the presence and absence of SSB.
• Investigation of RecA-ssDNA complex stability and dissociation.

Main Results:

• RecA protein and circular ssDNA form a stable complex with SSB, with a 1:2 RecA monomer to nucleotide ratio.
• These complexes are key intermediates in homologous strand exchange.
• RecA protein remains bound to the duplex product after strand exchange, while SSB binds the displaced strand.
• ADP addition triggers the dissociation of the RecA-duplex DNA complex.
• RecA protein binds ssDNA without SSB, but at a reduced level.

Conclusions:

• SSB protein directly participates in the formation of RecA-ssDNA complexes, confirming kinetic data.
• RecA protein can transition between bound and free states, even without SSB.
• The findings provide physical evidence for the dynamic interactions governing RecA-mediated DNA strand exchange.