Figure 5.

Summary and relationship to previous studies. (A) Chromatin fragments obtained by nuclease digestion of chromosomes associate spontaneously forming multilayer plates (represented as parallel shaded lines in the cross section; the red line corresponds to the carbon film substrate used for TEM imaging); part of the chromatin fragments form short 30-nm fibers that can be unfolded and incorporated into the growing plates (this association reaction is indicated with a discontinuous line). (B) The multilayered planar structures that were found in previous studies (13–17) sliding from partially denatured chromosomes were clearly visible in the electron micrographs (schematized in the left part of the chromatid cross section) and have the same structural characteristics as the laminar aggregates produced by self-assembly. The results obtained in this study demonstrating the spontaneous formation of planar metaphase chromatin strengthens the hypothesis that condensed chromosomes are formed by many stacked chromatin layers (represented in the right part of the chromatid cross section). The different structural elements schematized in this figure are not drawn at the same scale.