Role of PARP1 in DNA damage repair. PARP1 consists of a DNA-binding domain with 3 zinc finger motifs, an automodification domain that contains the BRCA1 C terminus (BRCT) domain, and a carboxy-terminal catalytic domain, which contains the active site of the enzyme. PARP1 is usually activated by DNA damage occurring as a result of the DNA damage response. The net result of its activation is the production of PAR chains, with the use of nicotinamide adenine dinucleotide (NAD⁺) as substrate. PARylation results in the recruitment of several proteins with multiple roles on DNA damage repair.