Figure 3.

Long pauses in the elongation dynamics are rarely followed by processive changes in the direction of transcription. (A) The extension of the transcribed product as a function of time. At 800 s (indicated by arrow), P2 RdRp exhibits a reversal behavior. The experimental conditions include an applied force of 16 pN force and an acquisition frequency of 25 Hz. (B) The probability of observing a reversal event as a function of the applied force (see panel (A)). The error bars represent the 95% confidence interval for a binomial distribution for the ordinate and the standard deviation of the applied force (±5%, see (50)) for the abscissa. (C and D) P2 RdRp transcription activity traces that exhibit very rare behavior in which multiple switches in the apparent directionality of the signal can be observed. In both panels, the extension of the RNA construct (1) increases, then (2) decreases (as in a reversal event) and (3) increases again. Data are acquired at an applied force of 25 pN using buffer conditions described in Materials and Methods. For panels (A), (C) and (D), raw data are shown in blue and data low-pass filtered at 0.5 Hz are shown in black.