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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.
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