Higher order structure in metaphase chromosomes. II. The relationship between the 250 A fiber, superbeads and beads-on-a-string.
The morphology of metaphase chromosome-derived chromatin fibers released from cells by non-ionic detergent cell lysis in the presence of divalent cations has been studied by electron microscopy. In these preparations the euchromatic arms appear as a series of loops, 200-300 A in diameter, which are composed of closely-apposed nucleosome arrays. The higher order fiber in chromosomes derived from detergent-lysed cells appears to be less stable than chromatin fibers obtained by mechanical cell lysis. The fiber breaks down into a series of non-uniform nucleosome aggregates (superbeads) and finally to chromatin in a beads-on-a-string morphology upon incubation at 31 degrees for 20 min. These observations allow us to suggest a relationship between uniform thick fibers, superbead-containing fibers, and beads-on-a-string chromatin within metaphase chromosomes.
D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002875:Chromosomes / Q000648:ultrastructure*; D008677:Metaphase; D051379:Mice; D008854:Microscopy, Electron