1) DNA of several hundred kb in size, labelled by a fluorescent intercalating dye, was shown to exhibit a) a distribution of condensed or linear conformations depending on buffer concentration during electrophoresis (1 V/cm, 25 degrees C); b) a variable conformation for a single DNA molecule during migration, changing from a roughly spherical to a V-shaped to an extended and back to a roughly spherical conformation; c) a migration rate varying from a maximal value for the spherical molecule down to zero for the symmetric V-shaped species; d) stretching of the V-shaped species while its migration rate decreases or increases. This migration behavior is interpreted as entanglement of an elastic molecule on the gel fiber, elastic stretching during entanglement and elastic disentanglement,and recoil concomitant with free migration until the cycle of entanglement and migration repeats itself. The entanglement can be at single or multiple locations on the DNA molecule. Elastic stretching at excessive field strength leads to breaking of the molecule. 2) Size, surface net charge and relative abundance of components (of a given size and charge) were determined for 21 polydisperse particle populations of protein-bacterial coat carbohydrate conjugates.
Aim of the characterization was to correlate relative immunogenicity of vaccine preparations directed against meningitis with these physical properties.