Initiation of synthesis of full-length plus-strand DNA by WT and L74V-M184V RTs. (A) Graphic representation of the system used to monitor the initiation of plus-strand DNA synthesis. Underlined letters indicate sites of chain termination. The dot defines the +1 position in the reaction. (B) Time course determination of the initiation of plus-strand DNA synthesis. The dNTP concentrations were 10 μM, and samples were removed every 20 s for 5 min (lanes 1 to 15). (C) Quantification of the data shown in panel B. The graphs show the time-dependent release from pausing at position +1. (D) Efficiency of initiation of plus-strand DNA synthesis in the presence of increasing concentrations of dNTPs. Lanes 1 to 11 show 5-min reactions in the presence of 0, 1.5, 3, 6, 12, 25, 50, 100, 200, and 400 μM (each) concentrations of the four dNTPs.