Fig. 2: Burst and step sizes for different substrates.

a Representative packaging traces at low force (7–12 pN) are shown for the four substrates at 2.5 kHz (gray) and are filtered to 100 Hz (colored). On A-form substrates, the dwell-burst coordination of the motor is retained but with a changed burst size. The dashed lines are spaced to match the mean burst size of the substrates. b Pairwise distance analysis of the trajectories confirms a decrease of the burst size for the three A-form substrates. The dashed lines are evenly spaced in multiples of the mean burst size. c Representative traces at high force (35–40 pN) resolves motor steps. For dsDNA, steps of 0.85 nm are observed; however, for A-form substrates, smaller steps are also seen every four steps. d Step-size distributions from packaging traces against high-force. Top: the step-size distribution of dsDNA and DTS hybrid peak at 0.85 nm (black dashed line). The striking similarity between maxima supports the interpretation that the burst adapts to the decreased helical pitch by modifying one of the four steps over the alternative model where the four steps are proportionally reduced. Would the latter be the case, the DTS hybrid step distribution would be expected to peak at 0.72 nm (magenta dashed line). Bottom: by taking the difference between the dsDNA and the DTS hybrid step-size distributions (black solid line), we observe two populations of steps whose means are 0.51 and 1.36 nm, respectively. These sizes are consistent with the size of the expected fourth reduced step and its combination with one regular 0.85 step, as if the two steps were combined during stepfinding. For all panels, [ATP] is 0.25 mM.