PARP is activated by DNA strand breaks. Upon activation, PARP catalyzes the transfer of ADP-ribose units from NAD+ (nicotinamide adenine dinucleotide) to target proteins, forming long branched chains of poly(ADP-ribose). This post-translational modification serves as a platform for the recruitment of DNA repair proteins like XRCC1, DNA ligase III, and DNA polymerase beta, which collaboratively restore DNA integrity.
