Cryo-electron microscopic visualization of RAD51 filament assembly and end-capping by XRCC3-RAD51C-RAD51D-XRCC2

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Homologous recombination is vital for DNA repair and replication fork protection.
• The precise roles of the five RAD51 paralogs in these processes are not fully understood.
• Mutations in RAD51 paralogs are associated with cancers and Fanconi anemia.

Purpose of the Study:

• To elucidate the distinct functions of RAD51 paralogs in DNA repair.
• To characterize the assembly and roles of RAD51 paralog complexes.
• To provide structural insights into RAD51 filament dynamics.

Main Methods:

• Cryo-electron microscopy to visualize complex structures.
• Biochemical assays to study complex assembly and function.
• Analysis of RAD51 paralog interactions.

Main Results:

• RAD51 paralogs assemble into two distinct heterotetrameric complexes: RAD51B-RAD51C-RAD51D-XRCC2 (RAD51B complex) and XRCC3-RAD51C-RAD51D-XRCC2 (XRCC3 complex).
• The RAD51B complex facilitates dynamic, ATP hydrolysis-dependent RAD51 filament assembly.
• The XRCC3 complex stably caps 5'-termini of RAD51 filaments, promoting homologous pairing.

Conclusions:

• The identified RAD51B and XRCC3 complexes have specialized functions in DNA repair and replication fork stabilization.
• These findings reveal mechanisms of RAD51 filament formation and capping.
• The conserved nature of these complexes highlights their fundamental importance in genome maintenance.