Fig. 3.

Mechanical unfolding of RNA structures by optical tweezers. (A) One type of optical tweezers. The RNA structure of interest is held between two micron-sized polystyrene beads by flanking the handles of RNA/DNA hybrids. One bead is placed in an optical trap for manipulation and force measurements. The figure is schematic and not to scale. (B) DU177 pseudoknot. The structure contains two stems (S1 and S2) and two loops (L1 and L2). Red dotted lines indicate five base triples and one noncanonical base pair. (C) Bimolecular design to mimic the DU177 pseudoknot. Pseudoknot is split into a hairpin (black) and an oligomer (blue) at the junction of S1 and L2. Expected direction of pulling force when the structure is placed on optical tweezers is indicated by arrows. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)