Single Molecule Studies Of Nucleic Acids And Their Proteins PDF Download

Nucleic acids--DNA and RNA--are critical to life, involved in the storage and decoding of genetic information in the cell as well as the regulation and catalysis of specific biological processes. The function of a nucleic acid molecule is determined in large part by the structure it adopts, which in turn depends on its sequence. The mechanisms of sequence-directed nucleic acid folding remain incompletely understood, particularly for large RNA molecules. The work presented in this thesis uses single-molecule optical-trapping techniques to study nucleic acid folding, where reversible folding is induced and measured in individual molecules through the application of force. In Chapter 2 we demonstrate direct measurement of the full folding energy landscapes of DNA hairpins, which comprise a model system for studying nucleic acid secondary structure, and show how such landscapes are sensitive to sequence. In Chapter 3 we study the electrostatics of DNA hairpin folding by measuring trends in folding energies under different ionic conditions and comparing these trends with those predicted by Poisson-Boltzmann theory. Finally, in Chapter 4 we examine folding of the TPP riboswitch aptamer, an RNA molecule with complex secondary structure that also adopts tertiary structure upon binding a small-molecule ligand. We measured the folding energy landscape of the aptamer and perturbations of this landscape resulting from mutations and ligand binding, and propose a kinetic model to describe the coupling between aptamer folding and ligand binding. Taken together, the results presented here demonstrate the usefulness of the energy landscape framework for characterizing nucleic acid folding in conjunction with single-molecule measurements.