Figure 4.

Activity of Pif1p on forked substrates at 25°C. (a) Structure of the forked substrates, using the same conventions as in Figure 2a. (b) Unwinding of fD20 and fR20 forked substrates in multiple cycle (– trap) and single cycle conditions (+ trap). (c) Quantification of three independent unwinding reactions of the fD20 and fR20 forked substrates. (+) and (–) indicate, respectively, reactions done in the presence and absence of a single-strand DNA trap. Amplitude and apparent turnover rates are as follows. Multiple cycle conditions: A_(fD20) = 92 ± 2%, k_(fD20) = 2.1 ± 0.3 min⁻¹; A_(fR20) = 93 ± 1%, k_(fR20) = 18.3 ± 2 min⁻¹. For single cycle kinetics, no unwinding was observed for the fD20 substrate; values for fR20 were A_(fR20) = 19 ± 1%, k_(fR20) = 5.2 ± 0.7 min⁻¹.