Figure 4.

Construction of a gap/lesion plasmid with an extended gap. Substrate GP21 was reacted with T7 exonuclease gp6 as described in Materials and Methods to generate GP21-L containing an extended gap of 350 nucleotides. A shows the substrate GP21 after exonuclease treatment and S1 treatment to determine the size of the ssDNA gap. B shows the analysis of the substrate by restriction with DraIII, which cuts once in the plasmid. The formation of a single full length DNA band indicates that substrates GP21 and GP21-L are circular. Restriction of linear control plasmid with DraIII generated two fragments each of ≈1.4 kbp, as expected.