Kinetic and Thermodynamic Factors Govern DNA Condensate Size and Morphology

It is well known that multivalent cations can cause DNA to condense from solution to form high-density nanometer scale particles. However, several fundamental questions concerning the phenomenon of DNA condensation remain unanswered. DNA condensation in vitro has been of interest for many years as a model of naturally occurring DNA packaging (e.g. chromatin, sperm head and virus capsid packing). More recently, DNA condensation has been of interest in optimizing artificial gene delivery, where packaging genes to an optimal size is essential to developing efficient uptake and delivery systems. The research presented in this dissertation provides an in depth biophysical study of the factors that control DNA condensate size and morphology. Millimolar changes in the ionic strength of the solution were found to alter the size of toroidal condensates. Variations in the order of addition of the counterions also significantly changed the size and morphology of the condensates. Studies were also performed to investigate the effects of static curvature and increased DNA flexibility on DNA condensation. These include the addition of static bending by sequence directed curvature, dynamic bending through protein-DNA interactions and reducing DNA persistence length by condensing single-stranded DNA. Several new models of DNA condensation are proposed based on the experimental data presented in this thesis.Ph.D