A synchrotron radiation X-ray scattering study of aqueous solutions of native DNA

Synchrotron radiation small-angle X-ray scattering (SAXS) was used to inves tigate solutions of native DNA at different ionic strengths and temperature s. The mass per unit length, radius of gyration of the cross-section of DNA and apparent second virial coefficient (A(2)) were obtained from Zimm plot s in the rodlike particle approximation. The values of A(2) obtained in thi s way are positive and almost constant indicating that the repulsive intera ctions still influence the scattering patterns at resolutions as high as 5- 8 nm. SAXS measurements in continuous temperature scans indicate that the r od approximation is valid over a wide temperature range during DNA melting and confirm that the rodlike-wormlike transition temperature increases with ionic strength.