Doping reactions with Vent starting with some correctly extended primer present in the reaction. See main text for more details. (A) Reaction seen with 25% of the starting material extended. Black circles, 0.5 μM dATP; red circles, 1 μM dATP; green triangles, 2 μM dATP; yellow triangles, 4 μM dATP; blue squares, 8 μM dATP. Reactions were carried out for 2 h. (B) Reaction seen with 75% of the starting material extended. Black circles, 0.5 μM dATP; red circles, 1 μM dATP; green triangles, 2 μM dATP; yellow triangles, 4 μM dATP; blue squares, 8 μM dATP. Reactions were carried out for 2 h.