Figure 1.

Experimental configuration and migration through a fully homologous Holliday junction. (A) A DNA tether with a preformed Holliday junction at its center was migrated under constant tension by rotation of a nanofabricated quartz cylinder using an angular optical trap. (Inset) Structure of a Holliday junction and directions of force and torque exerted on the vertical arms. (B) Individual extension and torque traces. Twenty negative turns were applied at ∼20 bp/s and then reversed, returning the junction to its original location. The end-to-end extension and the torque of each molecule were measured simultaneously. (C) Shown are the mean torque as a function of force (points) and theoretical prediction (line; not a fit).