X-ray diffraction studies of nucleohistone: a polyhelical model of chromosome organization.

The possibility that nucleohistone is constituted by a helical arrangement of DNA molecules is analyzed in this paper. A polyhelical model of nucleohistone in plectanemic double coils of variable dimensions is found to be compatible with the x-ray diffraction results obtained in this and other laboratories. The radius of the coils varies between 35 and 45 A, whereas the pitch varies between 200 and 120 A. Another part of nucleohistone is much less coiled and contributes to the "background" scattering of the sample. This model is compatible with a lampbrush organization of the chromosome.