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The three-dimensional structure of a double-stranded DNA molecule may be described by distinguishing the helical turns of the DNA duplex from any superhelical turns that might be superimposed upon the duplex turns. There are characteristic changes in the hydrodynamic properties of superhelical DNA molecules when they interact with intercalating agents. The hydrodynamic properties of nuclear structures released by gently lysing human cells are changed by intercalating agents in this characteristic manner. The characteristic changes are abolished by irradiating the cells with gamma-rays but may be restored by incubating the cells at 37 degrees C after irradiation. These results are interpreted as showing that human DNA is supercoiled. A model for the structure of the chromosome is suggested.

Type

Journal article

Journal

J Cell Sci

Publication Date

11/1975

Volume

19

Pages

261 - 279

Keywords

Binding Sites, Cell Nucleus, Centrifugation, Density Gradient, DNA, Neoplasm, Ethidium, Gamma Rays, HeLa Cells, Humans, Leucine, Nucleic Acid Conformation, Radiation Effects, Streptomycin, Thymidine