DNA Structures and Transitions: X-Ray Diffraction Studies of Solvated Fibers

The distinctive X-ray diffraction patterns of fibers provide a rich source of data. They are the basis for the original definitions of the conformations of DNA, except for the Z form, and can readily serve as “fingerprints” for their presence. Furthermore, simple measurements of layer line spacings in fiber patterns can often supply both of the individual helical parameters (pitch and rise per residue) needed to give the number of residues per turn (Zimmerman 1982).