FIGURE 7.

Accumulation of AP sites is associated with decreased AP endonuclease activity in GAPDH-deficient cells. A, genomic DNA was isolated from the control and GAPDH siRNA transfected cells and analyzed for abasic (AP) site lesions using the aldehyde reactive probe assay. The bar graph shows the number of AP sites detected per 100,000 base pairs. The means and standard deviation of three independent experiments are shown. B, total cell extracts (250–750 ng, lanes 3–5 and 6–8) from the indicated cells were monitored for AP enoduclease activity using the 42-mer substrate (80 ng). Shown are the substrate (lane 1) and purified Endo IV (lane 2). C, quantification of the formation of the 20-mer product in B. D, silver-stained gel showing equal amount of total protein in the extracts used for the AP endonuclease assay.