Enhanced ligation of repair sites under conditions of inhibition of poly(ADP-ribose) synthesis by 3-aminobenzamide.

The rate of intracellular ligation of excision-repair patches has been measured under conditions of inhibition of poly(ADP-ribose) synthesis by 3-aminobenzamide. Excision-repair patches in DNA of cells damaged by methyl methanesulfonate were labeled with [3H]thymidine and blocked at an intermediate stage by aphidicolin, an inhibitor of DNA polymerase alpha. Removal of [3H]thymidine and aphidicolin permitted the intracellular ligation rate to be determined by rapid digestion of [3H]-labeled 3' termini with exonuclease III. Contrary to previous conclusions from more indirect experiments, inhibition of poly(ADP-ribose) synthesis by 3-aminobenzamide actually facilitates rapid ligation.