Hydration of Nucleic Acids

Abstract

The conformation of DNA, but not of RNA, is determined by water activity. If salts or organic polar solvents are added to an aqueous solution of double helical RNA or DNA, the water activity changes and water molecules are withdrawn from the outer hydration shell. This has almost no influence on the molecular structure of RNA which under all conditions maintains its A-type conformation. It transforms only to a comparable A'-RNA with 12 instead of 11 nucleotides per double helix turn if the salt concentration is raised beyond a certain level.