ABSTRACT
The path of folding of the deoxyribonucleic acid (DNA) can be determined by electron microscopy, and the residual nonhistones which organize the histone-depleted chromosomes can be analyzed by polyacrylamide gel electrophoresis. Three major classes of macromolecules provide the basic components for the structural organization of metaphase chromosomes: DNA, histones, and nonhistone proteins. Other minor species such as ribonucleic acid and membrane lipids may also have important structural roles, but the fundamental chromosomal substructural must be determined by the predominant macromolecular species. The centromere, for example, must have a substructure which differentiates it from other parts of the chromosome. The isolation of histone-depleted metaphase chromosomes allows two basic aspects of chromosome structure to be investigated. Antiserum was prepared that was specific for HeLa cell chromatin, and not to chromatin from other human tissues and cell lines. Models of chromosome structure are difficult to compare since all models that have been presented to date are incomplete.
