Figure 19. DNA Devices.

(a) A Mobile Control Device. The cruciform structure on the left contains four mobile base pairs at its base. Addition of an intercalator (ethidium) unwinds the circle, moving them into it. Removal of the ethidium reverses the action of the device. (b) A DNA Nanomechanical Device Based on the B-Z Transition. The device consists of two DX molecules connected by a shaft containing 20 nucleotide pairs (yellow) capable of undergoing the B-Z transition. Under B conditions the short domains are on the same side of the shaft, but under Z-conditions (added Co(NH₃)₆³⁼) they are on opposite sides of the shaft. The pink and green FRET pair are used to monitor this change. (c) The Machine Cycle of a PX-JX₂ Device. Starting with the PX device on the left, the green strands are removed by their complements (Process I) to leave an unstructured frame. The addition of the yellow strands (process II) converts the frame to the JX₂ structure, in which the top and bottom domains are rotated a half turn relative to their arrangement in the PX conformation. Processes III and IV reverse this process to return to the PX structure. (d) AFM Demonstration of the Operation of the Device. A series of DNA trapezoids are connected by devices. In the PX state, the trapezoids are in a parallel arrangement, but when the system is converted to the JX₂ state, they are in a zigzag arrangement.