FIGURE 6.

Loading of Pol ϵ onto the 3′-primer terminus. Primer extension reactions were carried out by rapidly mixing enzyme with DNA, Mg²⁺, and dTTP and then quenching the reactions at the time points indicated in A. dTTP incorporation was indicative of ternary complex formation and subsequent phosphodiester bond formation. Different lengths of DNA substrates were used to monitor the length dependence on the accessibility for loading the 3′-primer terminus into the polymerase active site and to extend the primer by one nucleotide. The relative band intensities of the incorporation of dTTP (B) were plotted against time for Pol2 _core exo⁻ and Pol ϵ exo⁻.