It has been 25 years since the bihelical structure of DNA was proposed by Watson and Crick. The model was confirmed shortly after its conception, primarily by X-ray diffraction studies of DNA fibers. There are two major configurations. The A configuration has 11 bp per helical turn and the base pairs are tilted 20° from the perpendicular to the helix axis. The B configuration has 10 bp/turn and the base pairs are almost perpendicular to the helix axis. The B configuration is always found in fibers at high humidity, and it is generally agreed that in solution the DNA is in the B configuration.
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J. C. Wang (1979) studied this question.