Human PARP-1 (Poly(ADP-ribose)-Polymerase-1) bound to a DNA double strand break, molecular model. Human PARP-1 (Poly(ADP-ribose)-Polymerase-1) is a highly conserved protein (113 kDa) that is strongly activated by DNA strand breaks, and participates in modulating DNA base excision repair, apoptosis, and necrosis. It includes a DNA-binding domain with 23 zinc finger motifs, and a poly(ADP-ribose) polymerase catalytic domain