Fig. 1: Packaging of alternative substrates.

a The structure of the four substrates is shown, with DNA and RNA strands in light blue and light red, respectively. The strand being packaged from 5′ to 3′ is designated the tracking strand and its phosphates are colored dark red. Note the differing orientation of the phosphates for DNA and RNA strands, and the differing helical pitches (Table 1, red dotted lines span one pitch of dsDNA). b Single packaging complexes are held between two microspheres using a dual-trap optical tweezer, whereas the tether length is monitored over time. c Representative packaging trajectories for the four substrates are shown at 250 Hz. Dashed blue lines represent the velocity of packaging on dsDNA substrate. Reverse-translocation dynamics are observed on the RTS hybrid and dsRNA (black arrows). d Velocity distributions for the different substrates are curve fit to the sum of two gaussians (dark line), one with zero mean (curved dotted line) and one with positive mean (curved dashed line), which represent pausing and packaging, respectively. Vertical straight dotted lines mark the mean of the corresponding positive velocity gaussian fit. The right panel details negative velocities, which correspond to reverse-translocation dynamics. Note the increased probability of these events on dsRNA compared to the RTS hybrid. For all panels, [ATP] is 0.25 mM and opposing force is 7–12 pN.