Fig. 7. Summary of findings and model for RAD51D function as part of the BCDX2 and XRCC3 (X3CDX2) complexes.

a Summary of cellular findings. Schematic of RAD51D (1-328 aa) is shown with the Walker A and B motifs (green), and DNA binding loops (blue) indicated. The variants analyzed are shown above with the results from the cellular studies (MAVE variant-function map; Fig. 2), RAD51D Y2H interaction with XRCC2 and its Y3H interaction with RAD51C (Fig. 5), SCR recombination (HR), as well as olaparib and cisplatin clonogenic survival assays (Fig. 4) are summarized based on functional score. Loss-of-function is shown in red, an intermediate function is shown in yellow, and wild-type function is indicated in green. b Summary of biochemical findings. Variants included in biochemical analysis for BCDX2 or XRCC3 (X3CDX2) complex formation, DNA binding, ATPase restraint, and RAD51 strand exchange from Fig. 6 are shown. c Model for BCDX2 and X3CDX2 function in DSB repair. Upon DSB formation, the 3’ ssDNA end is resected and coated by RPA (a heterotrimeric protein complex, blue circles). The BCDX2 and X3CDX2 complexes facilitate the displacement of RPA and the loading of RAD51 (yellow circle) onto ssDNA. This is achieved by DX2 regulation of BC ATP hydrolysis, which facilitates its binding to ssDNA. CX3 in complex with DX2 then targets RAD51 to ssDNA. The combined functions of the BCDX2 and X3CDX2 complexes are necessary to facilitate RAD51 filament assembly. Subsequently, the X3CDX2 complex aids in the RAD51-mediated homology search and strand exchange activities needed for homologous recombination. RAD51D plays a critical role in both of these BCDX2 and X3CDX2 functions.