Do inhibitor studies demonstrate a role for poly(ADP-ribose) in DNA repair?

3-Aminobenzamide, an inhibitor of poly(ADP-ribose) synthesis, has been commonly used in attempts to demonstrate a regulatory role for the polymer during a late stage of repair. When a range of inhibitor concentrations was used paradoxical results were obtained. Up to 1 mM, 3-aminobenzamide appeared to reduce DNA break frequencies in cells damaged by methyl methane sulfonate; at doses of 2 mM and above, it appeared to increase break frequencies. In the high concentration range, many nonspecific side effects and cellular toxicity predominate. Evidence used to assert a role for poly(ADP-ribose) synthesis during ligation has usually been derived from experiments using high concentrations of 3-aminobenzamide, but these may be attributed to toxic side effects. 3-Aminobenzamide stimulates a large increase in repair replication which does not result from increased excision of damaged sites or an increased patch length but may be attributable to other cellular effects such as endogenous nuclease attack on DNA. The cellular effects of 3-aminobenzamide are therefore complicated by nonspecific effects over a commonly used concentration range and evidence for a specific regulatory role of poly(ADP-ribose) in DNA repair is weak.