Fluorescence-force spectroscopy maps two-dimensional reaction landscape of the holliday junction

Science. 2007 Oct 12;318(5848):279-83. doi: 10.1126/science.1146113.


Despite the recent advances in single-molecule manipulation techniques, purely mechanical approaches cannot detect subtle conformational changes in the biologically important regime of weak forces. We developed a hybrid scheme combining force and fluorescence that allowed us to examine the effect of subpiconewton forces on the nanometer scale motion of the Holliday junction (HJ) at 100-hertz bandwidth. The HJ is an exquisitely sensitive force sensor whose force response is amplified with an increase in its arm lengths, demonstrating a lever-arm effect at the nanometer-length scale. Mechanical interrogation of the HJ in three different directions helped elucidate the structures of the transient species populated during its conformational changes. This method of mapping two-dimensional reaction landscapes at low forces is readily applicable to other nucleic acid systems and their interactions with proteins and enzymes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacteriophage lambda
  • Biophysical Phenomena
  • Biophysics
  • DNA, Cruciform / chemistry*
  • DNA, Viral / chemistry
  • Fluorescence Resonance Energy Transfer
  • Nucleic Acid Conformation*
  • Optical Tweezers


  • DNA, Cruciform
  • DNA, Viral