An X-ray diffraction study of histone and protamine in isolation and in combination with DNA

An X-ray diffraction study of the basic proteins histone and protamine and of their complexes with DNA has been made with a view to elucidating the molecular structure of the proteins and of nucleohistone and nucleoprotamine. Isolated histone, when undenatured, gives diffuse diffraction rings in the regions of 4·5 and 10 A. In some patterns a sharp 4·7 A reflection is visible. In sheet specimens the direction of the 4·7 A spacing is parallel to the plane of the sheet and the 10 A spacing is perpendicular to the plane. The appearance of the diffuse diffraction patterns is compatible with the presence of α -helices; the sharp 4·7 A reflection probably arises from a β -type structure produced by denaturation. Protamine sulphate gives a strong diffuse ring at about 4·2 A and a weak ring at 7·5 A. Dry nucleohistone and nucleoprotamine give patterns similar to those of the isolated proteins.