Figure 2.
RPA binding induces the straightening of a 20-nt ssDNA. A, FRET histograms of the DNA substrate dT20 alone and with various concentrations of RPA. Each FRET histogram was constructed from more than 300 traces. B, representative FRET traces of dT20 in the presence of RPA. Black arrows indicate the addition of RPA. In 2 nm RPA, the dwell times at ∼E0.45 and ∼E0.25 (t1 and t2) were measured to characterize the different states of ssDNA in complex with RPA. C, both t1 and t2 follow a single-exponential decay with time constants of 2.1 and 18.1 s, respectively. D, after DNA association with RPA in the beginning, the fraction of FRET traces showing dynamic properties (RPA dissociation from ssDNA or switching to other binding modes) decreased significantly with increasing RPA concentration.