On the thymine-neighbor base short contacts in A-form of DNA

An idea of short contacts of thymine methyl group in A-form DNA is proposed to understand the structural changes of double helical DNA. To confirm the assumption that the unstable A-conformation needs lateral interactions, X-ray experiments on the complex of E. coli DNA with synthetic thermospermine in fiber were carried out. This complex showed the ordinary transition, except that it yielded a semicrystalline B-form at 66% r.h., suggesting good lateral interactions of the material by some number of cross-bridges of tetramine. This unstable factor is potentially of considerable biological interest.