Unwinding of box I substrate by UL9 protein and ICP8. The UL9 protein and increasing amounts of ICP8 were incubated with the box I substrate (2 pmol) for 60 min at 37°C. Lanes: 1, no protein; 2, boiled substrate; 3, UL9 protein alone; 4–8, 0.001, 0.01, 0.1, 1, and 10 pmol of ICP8 in the presence of the UL9 protein (2 pmol); 9–13, ICP8 in the absence of the UL9 protein.