PARP1 condensates differentially partition DNA repair proteins and enhance DNA ligation

Poly(ADP-ribose) polymerase 1 (PARP1) is one of the first responders to DNA damage and plays crucial roles in recruiting DNA repair proteins through its activity - poly(ADP-ribosyl)ation (PARylation). The enrichment of DNA repair proteins at sites of DNA damage has been described as the formation of a biomolecular condensate. However, it remains unclear how exactly PARP1 and PARylation contribute to the formation and organization of DNA repair condensates. Using recombinant human single-strand repair proteins in vitro, we find that PARP1 readily forms viscous biomolecular condensates in a DNA-dependent manner and that this depends on its three zinc finger (ZnF) domains. PARylation enhances PARP1 condensation in a PAR chain length-dependent manner and increases the internal dynamics of PARP1 condensates. DNA and single-strand break repair proteins XRCC1, LigIII, Pol beta, and FUS partition in PARP1 condensates, although in different patterns. While Pol beta and FUS are both homogeneously mixed within PARP1 condensates, FUS enrichment is greatly enhanced upon PARylation whereas Pol beta partitioning is not. XRCC1 and LigIII display an inhomogeneous organization within PARP1 condensates; their enrichment in these multiphase condensates is enhanced by PARylation. Functionally, PARP1 condensates concentrate short DNA fragments, which correlates with PARP1 clusters compacting long DNA and bridging DNA ends. Furthermore, the presence of PARP1 condensates significantly promotes DNA ligation upon PARylation. These findings provide insight into how PARP1 condensation and PARylation regulate the assembly and biochemical activities of DNA repair factors, which may inform on how PARPs function in DNA repair foci and other PAR-driven condensates in cells. By reconstituting early DNA repair proteins in vitro, this study shows how PARP1 organizes itself and other repair proteins around damaged DNA, leading to functional consequences in DNA end synapsis and ligation.PARP1 readily forms condensates in vitro in a manner dependent on DNA and its three tandem zinc finger motifs; autoPARylation enhances the formation and dynamics of PARP1 condensates.PARP1 differentially co-condenses nicked DNA and single-strand break repair factors FUS, XRCC1, LIG3, and POLB.PARP1 bridges broken DNA ends together and its activity in condensates enhances DNA ligation. By reconstituting early DNA repair proteins in vitro, this study shows how PARP1 organizes itself and other repair proteins around damaged DNA, leading to functional consequences in DNA end bridging and ligation.