Figure 1.

Pif1-catalyzed unwinding yielded differential product appearance in the presence or absence of DNA trap. (a) Duplex DNA substrate was mixed with Pif1 in the presence of ATP and MgCl₂ to form ssDNA product. A DNA trap complementary to the unlabeled strand was included in some reactions. (b) Unwinding experiments were initiated by mixing 2 nM 70T-30bp substrate, ATP, and MgCl₂ with 200 nM Pif1. Reactions were performed either in the absence (triangles) or in the presence (squares) of unlabeled 60 nM DNA trap. Fitting the data to the equation for a single exponential resulted in unwinding rate constants of 0.80 ± 0.02 and 1.3 ± 0.04 min^–1 for unwinding in the presence and absence of DNA trap, respectively. The amplitudes of the product formation curves are 0.87 ± 0.01 and 0.56 ± 0.01 for unwinding in the presence and absence of a DNA trap, respectively.