Fig. 4. Transdominant inhibition of DNA base excision repair by the N-terminal apoptotic fragment of PARP-1. DNA BER was assayed by monitoring the repair of oxy-radical damaged plasmids in whole cell extracts from the normal lymphoblastoid cell line GM01953C. (A) Agarose gel showing the repair of nicked plasmids (OC) following incubation in whole cell extract containing growing concentrations of the N-terminal apoptotic fragment of PARP-1. (B) Densitometric integration of the gel shown in (A). Repair is expressed as the proportion of repaired plasmids (CC) over the total amount of plasmids used in the repair reaction (OC+CC). Experiments were performed in the presence of a saturating concentration of NAD⁺ (2 mM).