Figure 3: PARP-1 mediates the repair of SSBs via the activation and recruitment of repair enzymes. Clockwise: PARP-1 binds to the DNA adjacent to the damage detecting and signaling the presence of an SSB. Once bound, PARP-1 catalyzes the cleavage of the coenzyme nicotinamide adenine dinucleotide (NAD+) into nicotinamide and ADP-ribose to produce highly charged branched chains of poly(ADP-ribose) (PAR). Then DNA ligase III (LigIII), DNA polymerase beta (polĪ²), and scaffolding proteins such as x-ray repair complementing gene 1 (XRCC1) are recruited to the site of damage, to repairing the damaged DNA. After repair, the PAR chains are degraded via PAR glycohydrolase (PARG).