Sanghwa Lee† and Sungchul Hohng *†
† Department of Physics and Astronomy, Department of Biophysics and Chemical Biology, and National Center for Creative Research Initiatives, Seoul National University, Seoul 151-747, Korea
*Correspondence: Sungchul Hohng
We developed a hybrid technique combining optical tweezers and single-molecule three-color fluorescence resonance energy transfer (FRET). In demonstrative experiments, we observed the force-sensitive correlated motion of three helical arms of a Holliday junction and identified the independent unfolding/folding dynamics of two DNA hairpins of the same length. With 3 times the number of observable elements of single-molecule FRET, this new instrument will enable the measurement of the complex, multidimensional effects of mechanical forces in various biomolecular systems, such as RNA and proteins.