Human RAD52 stimulates the RAD51-mediated homology search

Homologous recombination (HR) is a DNA repair mechanism of double strand breaks and blocked replication forks that involves a process of homology search and homologous pairing leading to the formation of synaptic intermediates whose architecture and dynamics are tightly regulated to ensure genome integrity. In this mechanism, RAD51 recombinase plays a central role and is supported by many partner including BRCA2 and RAD52. If the mediator function of BRCA2 to load RAD51 on RPA-covered ssDNA is well established, the role of RAD52 in HR, more precisely its interplay with BRCA2 is still far from understood. We have used Transmission Electron Microscopy combined with biochemistry to characterize the sequential participation of RPA, RAD52 and BRCA2 in the assembly of the RAD51 filament, its architecture and its activity. Despite our results confirm that RAD52 lacks a mediator activity, we observed that RAD52 can tightly bind to RPA-coated ssDNA, inhibit the mediator role of BRCA2 and form shorter RAD52- and RAD51-containing mixed filaments that are more efficient in subsequent homology search and formation of synaptic complexes and D-loops, resulting in more frequent multi-invasions as well. Through the characterization of the behavior of RAD52 and BRCA2, these results provide new molecular insights on the formation and regulation of presynaptic and synaptic intermediates during human HR.