FIGURE 4.

Steady-state and pre-steady-state kinetics of incorporation of dTTP opposite G and N²-alkyl G adducts by Dpo4. Dpo4 (70 nm) was incubated with 24-mer/36-mer primer·template complex (120 nm) in a rapid quench-flow instrument and mixed with 1 mm dTTP/5 mm MgCl₂ to initiate reactions. A, no bursts were observed for G (▪), N²-EtG (♦), N²-IbG (•), N²-BzG (□), N²-NaphG (▵), or N²-AnthG (▿). The linear rates (slope) were estimated: G, 0.40 ± 0.01 s^–1; N²-EtG, 0.10 ± 0.00 s^–1, N²-IbG, 0.047 ± 0.001 s^–1; N²-BzG, 0.030 ± 0.001 s^–1; N²-NaphG, 0.011 ± 0.000 s^–1; and N²-AnthG, 0.076 ± 0.003 s^–1). B, the presence of burst for incorporation of dTTP (▪) or (S_p)-dTTPαS (•) opposite N²-MeG. The data for N²-MeG were fit to a burst equation (Equation 1), and the others were fit to a linear equation. The rates for the incorporation of dTTP (▪) or (S_p)-dTTPαS opposite N²-MeG were, respectively, k_obs = 0.59 ± 0.11 s^–1 and k_obs = 0.61 ± 0.09 s^–1.