[Nucleotides in rat liver cells: sedimentation and fluorescence analysis; DNA, associated with residual nuclear...

Rat hepatocyte nucleoids, obtained at different conditions, have been studied by sedimentation and fluorescence methods. Divalent metal ions have been found to play an important role in the superhelical organization of nuclear DNA. Depending on nucleoid isolation conditions, different DNA fragments become associated with the residual nuclear structure. In rapidly sedimenting nucleoids, where nuclear DNA exhibits greater compaction, two types of DNA fragments, differing is size, are associated. In slowly sedimenting nucleoids, where nuclear DNA is in a more relaxed state, one type of DNA fragments is associated. It is assumed that nuclear DNA compaction is conditioned by the formation of additional DNA binding sites with residual nuclear structures and involves divalent metal ions. It has been shown with the aid of restrictase analysis that both types of DNA fragments contain different repeated nucleotide sequences.