Figure 5. The efficiency of AP site cleavage by extracts from NMR and mouse cells with different post-irradiation time. Reaction mixtures contained 100 nM 5'-[32P] 32-mer AP DNA, 0.5 mg/ml of cell extract and buffer components. The reaction proceeded at 37ºC for 10 min and then was quenched by addition of EDTA (20 mM final) followed by stabilization of intact AP sites with NaBH4 treatment. DNA was then analyzed as described in the section ‘AP site cleavage activity of cell extracts’. C1 – incubation of AP DNA in the absence of cell extracts reflects the level of spontaneous AP site cleavage. C2 – incubation of AP DNA with 100 µM NaOH that brings about full AP site cleavage.