In the last two decades, new methodologies that are able to assess DNA damage have been developed.
In 1976Cook et al. published a paper investigating the nuclear structure based on the lysis of cells with nonionic detergent and high-molarity sodium chloride. This treatment removes membranes, cytoplasm, and nucleoplasm, and disrupts nucleosomes, almost all histones being solubilized by the high salt. What is left is the nucleoid, consisting of a nuclear matrix or scaffold composed of RNA and proteins, together with the DNA, which is negative supercoiled as a consequence of the turns made by the double helix around the histones of the nucleosome. The survival of the supercoils implies that free rotation of the DNA is not possible. Cook et al. proposed a model with the DNA attached at intervals to the matrix so that it is effectively arranged as a series of loops, rather than as a linear molecule. When the negative supercoiling was unwound by adding intercalating agent (i.e. ethidium...
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