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Single-molecule manipulation and visualization techniques are particularly well suited to the study of biological systems. For example, single-molecule DNA manipulation experiments have yielded remarkable insights into the mechanisms of topoisomerases, helicases, and other nucleic acid enzymes that would be difficult or impossible to obtain with traditional biochemical methods. Following the activity of a single enzyme over time can reveal transient phenomena, fluctuations in activity, and the presence of enzyme sub-populations or enzymatic states, all of which are obscured by the averaging inherent in traditional ensemble measurements.

Magnetic and optical manipulation permit the application of controlled loads and rotations on individual DNA molecules, while simultaneously measuring displacements on the order of a nanometer or less. These techniques afford precise control of the topology and structure of DNA, while providing a real-time recording of protein activity, revealed by changes in DNA extension. More recently, these techniques have been combined with single-molecule fluorescence visualization, which offers the possibility of simultaneously observing a protein conformational or biochemical transition and its associated mechanical transition, in addition to the ability to monitor the composition and activity of multi-protein complexes.

We employ and develop novel single molecule techniques including optical and magnetic tweezers and fluorescence imaging, along with conventional molecular biology approaches to address fundamental questions pertaining to nucleic acids and nucleic acid enzymology. Current projects include the visualization of DNA topology and dynamics, mechanistic study of type II topoisomerases, and the characterization of multi-enzyme complexes interacting with DNA.