The conformation of a B-DNA decamer is mainly determined by its sequence and not by crystal environment.

By comparing the conformations adopted by a double-stranded decameric B-DNA fragment in different crystal environments, we address the question of the degree of deformability of DNA helices. The three-dimensional structure of the self-complementary DNA decamer CCAGGCmeCTGG has been determined from crystals of space group P6 at 2.25 A resolution with an R value of 17.2% for 2407 1 sigma structure amplitudes. The oligonucleotide forms a B-type double helix with a characteristic sequence-dependent conformation closely resembling that of the corresponding unmethylated decamer, the structure of which is known from a high-resolution analysis of crystals of space group C2. Evidently, both the effects of single-site methylation and altered crystal environment on the DNA conformation are small. Therefore, double-helical DNA may possess sequence-determined conformational features that are less deformable than previously thought.