DESCRIPTION: This amended new application seeks funding to characterize features of DNA electrostatics by observation of the free solution mobilities of a number of DNA molecules. The first goal is to measure the effect of net charge on the migration of DNA in an electric field. The second is to investigate the sequence dependence of the effective charge on the DNA molecule, following up on preliminary work indicating that this is the case. Combined with FRET analysis, the experiments proposed will challenge the hypothesis that monovalent counterion binding in the minor groove of DNA causes electrostatic collapse and leads to bending towards the minor groove. Further work entails an examination of the interaction between DNA and commonly used buffers in electrophoresis experiments.