Evidence for the existence of stable curvature of DNA in solution.

A 121-base-pair DNA restriction fragment derived from the kinetoplast minicircle, Lt19, of Leishmania tarentolae displays substantially abnormal electrophoretic behavior on polyacrylamide gels. The electrophoretic behavior of a series of palindromic dimers containing all or part of the 121-base-pair fragment has been used to establish that curvature of the DNA helix is the basis of the abnormal behavior. One of the palindromic dimers, KP242, has been examined in more detail by using the technique of differential decay of birefringence (DDB). The technique consists of analyzing the difference in the rates of decay of birefringence for two DNA fragments, each consisting of an identical number of base pairs, and is capable of resolving differences in length as small as 1%. This approach has yielded an estimate for the apparent curvature of the dimer which, when represented as an equivalent rod with a single bend at its center, equals approximately 52 degrees. DDB measurements made at several ionic strengths indicate that a substantial portion of the curvature is static, rather than a simple consequence of increased flexibility.