Cooperation between salt induced globule-coil transition in single duplex DNA complexed with cationic surfactant and sphere-rod transition of surfactant micelles

The effect of low-molecular salt, sodium bromide (NaBr), on the conformational behavior of T4DNA globules, compacted with cetyl trimethylammonium bromide (CTAB), was studied in aqueous buffer solution. The conformational dynamics of individual single duplex T4DNA molecules was visualized directly with the use of fluorescence microscopy (FM), whereas viscometry was used for monitoring of the surfactant structure in the aqueous media. We have found that DNA globules, compacted with CTA, are unfolded into the elongated cell state with the increase of NaBr concentration, exhibiting the character of a discrete first-order phase transition. It is indicated that, accompanied with the increase of NaBr concentration, the unfolding transition is induced simultaneously with the sphere-rod transition of surfactant micelles. These results clearly indicate the cooperative effect between two different types of transitions.