Polymorphism in B-DNA: X-ray diffraction studies on Li-DNA fibres

Abstract

From X-ray diffraction studies it is generally believed that B-DNA has the structural parameters n=10 and h=3.4 Å. However, for the first time we report that polymorphism in the B-form can be observed in DNA fibres. This was achieved by the precise control of salt and humidity in fibres and by the application of the precession method of X-ray diffraction to DNA fibres. The significant result obtained is that n=10 is not observed for crystalline fibre patterns. In fact, n=10 and h=3.4 Å are not found to occur simultaneously. Instead, a range of values, n=9.6-10.0 and h=3.35 Å-3.41 Å is observed.