ROLE OF POLY(ADP-RIBOSE) FORMATION IN DNA-REPAIR

THE abundant nuclear enzyme poly(ADP-ribose) polymerase catalyses the synthesis of poly(ADP-ribose) from nicotinamide adenine dinucleotide (NAD+) 1-5. This protein has an N-terminal DNA-binding domain containing two zinc-fingers, which is linked to the C-terminal NAD+-binding domain by a short region containing several glutamic acid residues that are sites of auto-poly(ADP-ribosyl)ation 6-8. The intracellular production of poly(ADP-ribose) is induced by agents that generate strand interruptions in DNA 7. The branched homopolymer chains may attain a size of 200-300 residues 9 but are rapidly degraded after synthesis. The function of poly(ADP-ribose) synthesis is not clear, although it seems to be required for DNA repair 10,11. Here we describe a human cell-free system that enables the role of poly(ADP-ribose) synthesis in DNA repair to be characterized. The results indicate that unmodified polymerase molecules bind tightly to DNA strand breaks; auto-poly(ADP-ribosyl)ation of the protein then effects its release and allows access to lesions for DNA repair enzymes.