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James L. Sims,** Sosamma J. Berger, 8and Nathan A. Berger*· 8 abstract: Inhibitors of poly (ADP-ribose) polymerase stimulated the level of DNA, RNA, and protein synthesis in DNA-damaged LI210 cells but had negligible effects in un-damaged LI210 cells. Thepoly (ADP-ribose) polymerase inhibitors stimulated DNA repair synthesis after cells were exposed to high concentrations of TV-methyl-iV'-nitro-A-nitrosoguanidine (68 and 136 µ) but not after exposure to low concentrations (13.6 and 34 µ). When the L1210 cells were exposed to 136 µ jV-methyl-JV'-nitro-N-nitrosoguanidine, the activation of poly (ADP-ribose) polymerase resulted in the rapid depletion of oxidized nicotinamide adenine dinucleotide (NAD+) levels and subsequent depletion of adenosine S'-triphosphate (ATP) pools. After low doses of i^ x> ly (ADP-ribose) 1 polymerase, a chromatin-bound enzyme, cleaves NAD+ to yield nicotinamide and ADP …