PULLING MORE GENTLY

Many biological processes may involve subtle conformational changes in response to weak and transient forces, but experimental
limitations have confined studies of single molecules to examining the effect of relatively large forces. Hohng et al. (Science 318, 279) have developed a hybrid force and fluorescence spectroscopy that can monitor nanometer-scale conformational changes in single molecules that occur in response to sub-piconewton forces. They used this approach to gain insight into the reaction landscape of the Holliday junction by gently stretching it along different directions and monitoring fluorescence resonance energy transfer.