uri physics colloquium: Cruickshank Lecture

Optical Tweezers:  Gene Regulation, Studied One Molecule at a Time

Steven M. Block,S.W. Ascherman Professor of the Sciences, Department of Applied Physics, Department of Biology, Stanford University, CA, USA

abstract

Recent advances have led to the new field of single molecule biophysics. Single-molecule techniques can record characteristics that are obscured by traditional biochemical approaches, revealing the behaviors of individual biomolecules. Prominent among the new techniques is the laser-based optical trap, or ‘optical tweezers,’ which relies on radiation pressure to manipulate molecules. Optical traps can now measure biomolecular properties with a precision down the atomic level—achieving a resolution of 1 angstrom over a bandwidth of 100 Hz—while exerting controlled forces in the piconewton range. Among the successes for optical traps have been measurements of the molecular steps produced by motor proteins (for example, kinesin and myosin) and by processive nucleic-acid enzymes (for example, RNA polymerase), determinations of the strengths of the noncovalent bonds between proteins, and studies of the energetics and kinetics of structure formation by nucleic acids. Optical trapping instruments have been particularly useful in mapping the energy landscapes of folding for structured RNA molecules. Beyond that, we’re now able to follow the co-transcriptional folding of RNA in real time, as it’s synthesized, revealing how such folding can regulate downstream genes, mediated by elements called riboswitches. In recent developments, optical traps have been used in conjunction with single-molecule FRET (Förster Resonance Energy Transfer) to report simultaneously on the folding configurations and internal degrees of freedom of biomolecules.