Visualization of direct and diffusion-assisted RAD51 nucleation by full-length human BRCA2 protein.

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Homologous recombination (HR) is vital for repairing DNA double-strand breaks and replication stress.
• BRCA2 protein acts as a recombination mediator, initiating HR by facilitating RAD51 nucleation on ssDNA.
• The role of BRCA2's double-stranded DNA (dsDNA) binding in RAD51 loading remains largely uncharacterized.

Purpose of the Study:

• To investigate the function of BRCA2's dsDNA binding in the context of RAD51 nucleation.
• To elucidate the real-time mechanisms of BRCA2-mediated RAD51 loading onto ssDNA using purified proteins.

Main Methods:

• Single-molecule (SM) imaging techniques were employed to visualize protein interactions in real time.
• Purified BRCA2 and RAD51 proteins were utilized to study the nucleation process in vitro.

Main Results:

• BRCA2 directly nucleates and stabilizes RAD51 on ssDNA.
• A novel diffusion-assisted mechanism was identified, where BRCA2 binds and slides along dsDNA to deliver RAD51 to ssDNA.
• This dsDNA-dependent loading requires the coordinated action of multiple dsDNA-binding domains within BRCA2.

Conclusions:

• BRCA2 employs at least two distinct pathways for RAD51 loading onto ssDNA: direct nucleation and dsDNA-mediated delivery.
• These dual mechanisms highlight BRCA2's complex role in ensuring efficient DNA repair and maintaining genome integrity.
• Understanding these mechanisms is critical for comprehending BRCA2's tumor suppressor functions.