title: Electron-microscopy of intact nuclear DNA from human cells.
abstract: Structures retaining many of the morphological features of nuclei may be released by lysing human cells in a non-ionic detergent and 2 M NaCl. Such nucleoids contain all the nuclear DNA packaged within a flexible cage of RNA and protein. HeLa nucleoids have been spread at an air-water interface and viewed in the electron microscope. A tangled network of superhelical fibres surrounds the collapsed cage. Irradiation with gamma-rays abolishes supercoiling and treatment with the untwisting enzyme or a low concentration of ethidium reduces it. A high concentration of ethidium induces supertwisting. The nuclear DNA of higher cells can be isolated naked, supercoiled and intact.
mesh_terms: D002467:Cell Nucleus / Q000032:analysis; D004264:DNA Topoisomerases, Type I / Q000494:pharmacology; D004278:DNA, Superhelical / Q000302:isolation & purification / Q000528:radiation effects; D004996:Ethidium / Q000494:pharmacology; D005720:Gamma Rays; D006367:HeLa Cells; D006801:Humans; D008854:Microscopy, Electron; D009690:Nucleic Acid Conformation / Q000187:drug effects
chemical_list: D004278:DNA, Superhelical; D004264:DNA Topoisomerases, Type I; D004996:Ethidium