B-Z conformational transition and hydration of poly (dC-dG).poly (dC-dG) in fibres

The B-Z transition of poly(dC-dG).poly(dC-dG) has been studied by fibre X-ray diffraction and measurement of fibre dimensions. The polymorphism of the Z form is well observed as a function of variations of the r.h. (relative humidity). The Z to B transition is obtained at very high r.h. values. The cooperative transition from B to Z is associated with a disorganization of the fibre. Details about the hydration of the polynucleotide during conformational transitions are presented and it is shown that a nucleotide in Z form can be associated with up to 16 water molecules and up to 22 when in the B form.