Divalent and multivalent cations control liquid-like assembly of poly(ADP-ribosyl)ated PARP1 into multimolecular associates in vitro

The formation of nuclear biomolecular condensates is often associated with local accumulation of proteins at a site of DNA damage. The key role in the formation of DNA repair foci belongs to PARP1, which is a sensor of DNA damage and catalyzes the synthesis of poly(ADP-ribose) attracting repair factors. We show here that biogenic cations such as Mg²⁺, Ca²⁺, Mn²⁺, spermidine³⁺, or spermine⁴⁺ can induce liquid-like assembly of poly(ADP-ribosyl)ated [PARylated] PARP1 into multimolecular associates (hereafter: self-assembly). The self-assembly of PARylated PARP1 affects the level of its automodification and hydrolysis of poly(ADP-ribose) by poly(ADP-ribose) glycohydrolase (PARG). Furthermore, association of PARylated PARP1 with repair proteins strongly stimulates strand displacement DNA synthesis by DNA polymerase β (Pol β) but has no noticeable effect on DNA ligase III activity. Thus, liquid-like self-assembly of PARylated PARP1 may play a critical part in the regulation of i) its own activity, ii) PARG-dependent hydrolysis of poly(ADP-ribose), and iii) Pol β-mediated DNA synthesis. The latter can be considered an additional factor influencing the choice between long-patch and short-patch DNA synthesis during repair.