Research shows that RAD51 paralogs assemble into two distinct heterotetrameric complexes: RAD51B-RAD51C-RAD51D-XRCC2 (RAD51B complex) and XRCC3-RAD51C-RAD51D-XRCC2 (XRCC3 complex).[2][3] The RAD51B complex promotes the dynamic assembly of RAD51 filaments dependent on adenosine triphosphate (ATP) hydrolysis.[1][2][3] Conversely, the XRCC3 complex stably closes the 5'-ends of RAD51 strands on single-stranded DNA, double-stranded DNA with a tail and D-loop intermediates.[1][2] These structures were visualized by cryo-electron microscopy (cryo-EM) at 2.7 Å resolution for a presynaptic filament composed of five RAD51 protomers associated with the XRCC3 complex.[1] XRCC3 directly interacts with RAD51 and XRCC2 forms a cap.[1] The complexes are highly conserved in evolution and contribute to DNA double-strand break repair and replication fork stabilization.[1][2][3] Mutations in RAD51 paralogs are associated with hereditary breast and ovarian cancers and Fanconi anemia.[3]