Sedimentation of homogeneous double-strand DNA molecules.

Sedimentation velocity studies have been carried out with isolated double-strand DNA fragments prepared by digestion of PM2 phage with the restriction endonuclease Hae III. The results show that DNA molecules shorter than about 200 base pairs behave almost exactly as rigid rods with a diameter of 27 A. The behavior of the larger fragments (up to 1735 base pairs) can be described very well by either the theory of Yamakawa and Fujii (Yamakawa, H., and Fujii, M. (1973), Macromolecules 6. 407) using the same diameter and a persistence length of 575 A, or the theory of Hearst and Stockmayer (Hearst, J.E., and Stockmayer, W.H. (1962), J. Chem. Phys. 37, 1425) using a diameter of 20 A and a persistence length of 525 A.