Supplementary information
From the following article:
Structural transitions and elasticity from torque measurements on DNA
Zev Bryant, Michael D. Stone, Jeff Gore, Steven B. Smith, Nicholas R. Cozzarelli and Carlos Bustamante
Nature 424, 338-341(17 July 2003)
doi:10.1038/nature01810
Supplementary Movie 1: Assembly of the experimental system. The molecular construct is stretched between an anti-DIG bead on the micropipette and an anti-fluorescein bead held in buffer flow (right to left). A 520 nm streptavidin-coated bead is held in the optical trap in the lower portion of the screen. The stage is moved to position the biotinylated portion of the molecule near the streptavidin bead, which becomes attached to the DNA and is pulled out of the trap. The lower bead is then placed in the trap to complete the assembly of the system (Fig. 1b). In the final half of the movie, the tension on the molecule is repeatedly increased to ~65 pN. Overstretching occurs in the lower DNA segment but not the upper segment, confirming the existence of a nick below the bead (allowing the DNA to unwind and enter the overstretched state) but not above it. Bead rotation is inhibited by flow.
Supplementary Movie 2: 520 nm bead rotation during relaxation of an overwound molecule. A molecule with a 520 nm rotor bead was overwound as in Figure 1b. The movie begins subsequent to release of the rotor. The bead rotates at constant velocity for the first ~35 s, due to constant-torque conversion of P-DNA to B-DNA. Next, the angular velocity decays as torque and twist are removed from the molecule. Constant tension was maintained at 45 pN.
Supplementary Movie 3: Constant-torque rotation powered by the P-B transition is shown for a 760 nm rotor bead. Constant tension was maintained at 45 pN. Off-axis alignment of outer beads is due to an eccentric DNA attachment point; DNA is held vertically as judged by the absence of horizontal force.
Supplementary Movie 4: Overstretching and rewinding. Overstretching and rewinding is shown for a molecule with a 400 nm rotor bead (see Figure 3a). During the first ~26 s of the movie, the molecule is held at 85 pN and the bead rotation reflects unwinding of the molecule during the B-S transition. The separation of the beads increases at constant tension as the molecule converts to the longer S form. During the last part of the movie, the molecule is relaxed to 15 pN and the bead rotates in the opposite direction as the molecule rewinds. The movie is 2X actual speed.
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