Evidence for the persistence of a decondensed chromosome scaffold in the interphase nucleus

Nuclei of in vitro cultured bovine liver cells, deprived of the membranes by Triton X-100, were treated with 2 M-NaCl and DNase. Changes in ultrastructure and protein composition were studied at successive steps during treatment. Electron micrographs of nuclei treated with 2 M-NaCl showed a peripheral lamina and an internal system of randomly coiled filaments embedded in a mass of DNA fibres. After partial removal of the DNA the filaments could be seen to serve as backbones for the DNA attachment. Artificial redistribution occurring during fixation with glutaraldehyde suggests that the salt-resistant filaments are not stably cross-bridged into a three-dimensional network. The existence of reversible cross-bridges in vivo cannot be excluded, however. From the available data it is inferred that the filaments represent a decondensed from of the chromosome scaffolds and play a basic role in the organization of the genome throughout the nuclear cycle.