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. Author manuscript; available in PMC: 2010 Apr 15.
Published in final edited form as: Curr Opin Chem Biol. 2008 Sep 9;12(6):640–646. doi: 10.1016/j.cbpa.2008.08.011

Figure 1.

Figure 1

Representative SMFS measurements. (a) An RNA molecule is attached to two “handles” bound to beads and manipulated using two optical traps. Unfolded RNA is stretched by the force applied between the traps. As RNA unfolds or refolds, the resulting extension change is monitored. (b) FECs for the HIV TAR hairpin. After unfolding in a single step (black), the hairpin refolds through multiple intermediate states (red), producing hysteresis. Occasionally, an unfolded hairpin refolds partially to a metastable misfolded state (blue), as revealed by the return to the fully-folded state in a subsequent unfolding curve (green). Adapted from [12•]. (c) Extension of a model DNA hairpin at equilibrium under constant force, using a passive force clamp. The G:C content of the stem sequence was engineered to produce a landscape containing a metastable, partially-folded intermediate.