Regulation of DNA Strand Displacement Using an Allosteric DNA Toehold.

Toehold-mediated DNA strand displacement is the fundamental basis for the construction and operation of diverse DNA devices, including circuits, machines, sensors, and reconfigurable structures. Controllable activation and regulation of toeholds are critical to construct devices with multistep, autonomous, and complex behaviors. A handful of unique toehold activation mechanisms, including toehold-exchange, associative toehold, and remote toehold, have been developed and are often combined to achieve desired strand displacement behaviors and functions. Here we report an allosteric DNA toehold (A-toehold) design that allows the flexible regulation of DNA strand displacement by splitting an input strand into an A-toehold and branch migration domain. Because of its simplicity, the A-toehold mechanism can be a useful addition to the current toolbox of DNA strand displacement techniques. We demonstrated that A-toehold enabled a number of interesting functions that were previously shown using more sophisticated DNA strand displacement systems, including (1) continuously tuning the rate of strand displacement, (2) dynamic control of strand displacement reactions, and (3) selective activation of multiple strand displacement reactions. Moreover, by combining A-toehold and toehold-exchange mechanisms, we have successfully constructed a noncovalent DNA catalysis network that resembles an allosteric enzyme.