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J Biol Chem. 1993 Mar 15;268(8):5480-7.

NAD(+)-dependent repair of damaged DNA by human cell extracts.

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Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms, Hertfordshire, United Kingdom.


Rejoining of DNA single-strand breaks generated by treatment of plasmids with gamma-rays, neocarzinostatin, or bleomycin was catalyzed inefficiently by human cell extracts. The reaction was strongly promoted by the addition of NAD+, which was employed for rapid and transient synthesis of poly(ADP-ribose). The DNA rejoining reaction was accompanied by DNA repair replication, apparently due to replacement of damaged residues at termini. Selective depletion of poly(ADP-ribose) polymerase from cell extracts improved the repair of DNA exposed to a variety of DNA-damaging agents by removing the NAD+ dependence of the repair reaction. NAD(+)-promoted DNA repair by soluble cell extracts also occurred with alkylated DNA as substrate and was suppressed by 3-aminobenzamide. A similar stimulatory effect by NAD+ was observed for repair of ultraviolet-irradiated DNA, and this could be ascribed to the presence of pyrimidine hydrates as minor radiation-induced DNA lesions. No effect was observed on the sealing of gamma-irradiated DNA by supplementation of cell extracts with purified mammalian DNA ligase I or DNA ligase II. The results indicate that poly(ADP-ribose) polymerase interferes with base excision-repair processes because bound enzyme molecules block DNA strand interruptions. Release of bound poly-(ADP-ribose) polymerase following automodification, or physical removal of the protein from reaction mixtures, facilitates DNA repair.

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