Figure 3.

Active site titration of Dpo4 at 56°C. Dpo4 (30 nM) was preincubated with various concentrations of 5′-[³²P]-labeled-D-1 and subsequently mixed with a solution containing dTTP. The reactions were quenched after 26 ms and the products were analyzed by sequencing gel electrophoresis. The resulting burst amplitudes were plotted as a function of substrate concentration and fit to Equation (5) (Materials and Methods section) which gave a K_d for the Dpo4•D-1 complex of 39.9 ± 6.3 nM.