Figure 9: The effect of the position of the THF abasic site lesion within the A4 tract on the insertion and extension by Klenow fragment (exo+) (K) and T7 Sequenase (T7). The location of the THF lesion (X) is shown below the lane. The primer (Table 1, P20) is shown paired to a partial sequence of the template. There is no bypass of the THF-modification using the proofreading Klenow polymerase. When T7 Sequenase is used, the extent of stalling and extended product is dependent on the position of the lesion within the A-tract.