Crystallization of DNA from dilute solution.

Hexagonal platelet crystals about 1 mu across and about 150 A thick have been precipitated by the addition of ethanol to solutions of ultrasonically degraded, salmon sperm DNA in sodium cacodylate buffer. X-ray powder diffraction patterns from concentrated slurries of these crystals in mother liquor show intense rings at 23.9 A and at about 3.4 A; the former arise from lateral packing and the latter from an axial periodicity of the DNA helix. Evidence is presented to indicate that native DNA helices crystallize by chain folding and that no irreversible denaturation results from the crystallization process.