Conformation of Single-Stranded DNA in Aqueous Solution

The conformation of thermally denatured single-stranded DNA was studies by size exclusion chromatography equipped with a multi-angle light scattering on-line detector (SEC-MALS) and small angle X-ray scattering (SAXS). A sonicated sodium salt DNA sample from salmon testes dissolved in 0.015 M aqueous NaCl was kept at 85 degrees C for 10min, and then cooled to 10 degrees C at different ionic strengths before SEC-MALS and SAXS measurements. The results were analyzed using the wormlike chain or wormlike cylinder model to determine the contour length per nucleotide unit, the persistence length representing the polymer chain stiffness, and the chain thickness. The parameters obtained indicate that the single-stranded DNA chain is a typically flexible polyelectrolyte, of which conformation does not take the fully extended conformation but locally helical conformation.