Fig. 2

Conformational nucleic acid replicators. Two stable hairpins, H1 and H2, could potentially form a longer, double-stranded molecule, H1:H2 (bottom left). However, they are kinetically trapped. Addition of a catalyst strand (C1) leads to invasion and strand displacement of H1 (letter a), revealing a “toehold” region (3*). 3* can in turn invade H2 (letter b), ultimately resulting in release of C1 (letter c) and a repeat of the cycle