Temporal dynamics of base excision/single-strand break repair protein complex assembly/disassembly are modulated by the PARP/NAD(+)/SIRT6 axis

Assembly and disassembly of DNA repair protein complexes at DNA damage sites are essential for maintain-ing genomic integrity. Investigating factors coordinating assembly of the base excision repair (BER) proteins DNA polymerase 0 (Pol0) and XRCC1 to DNA lesion sites identifies a role for Pol0 in regulating XRCC1 disas-sembly from DNA repair complexes and, conversely, demonstrates Pol0's dependence on XRCC1 for com-plex assembly. LivePAR, a genetically encoded probe for live-cell imaging of poly(ADP-ribose) (PAR), reveals that Pol0 and XRCC1 require PAR for repair-complex assembly, with PARP1 and PARP2 playing unique roles in complex dynamics. Further, BER complex assembly is modulated by attenuation/augmentation of NAD+ biosynthesis. Finally, SIRT6 does not modulate PARP1 or PARP2 activation but does regulate XRCC1 recruit-ment, leading to diminished Pol0 abundance at sites of DNA damage. These findings highlight coordinated yet independent roles for PARP1, PARP2, and SIRT6 and their regulation by NAD+ bioavailability to facilitate BER.