title: An activity from mammalian cells that untwists superhelical DNA--a possible swivel for DNA replication (polyoma-ethidium bromide-mouse-embryo cells-dye binding assay).
abstract: Nuclei from secondary mouse-embryo cells contain an activity capable of untwisting closed-circular DNAs containing either negative or positive superhelical turns. The activity has no apparent effect on a closed-circular DNA containing no superhelical turns, and is not due to the combined action of an endonuclease and polynucleotide ligase. The enzyme apparently acts by introducing a single-strand nick into the DNA, forming a DNA-enzyme complex that allows the strands to rotate relative to the helix axis before reversing the reaction and sealing the break. The enzyme might possibly serve as a swivel during DNA replication.
mesh_terms: D000818:Animals; D002247:Carbon Isotopes; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D002499:Centrifugation, Density Gradient; D003470:Culture Media; D004261:DNA Replication; D004279:DNA, Viral / Q000302:isolation & purification / Q000378:metabolism*; D004622:Embryo, Mammalian; D066298:In Vitro Techniques; D007668:Kidney; D051379:Mice; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D010617:Phenanthridines / Q000494:pharmacology; D011120:Polyomavirus / Q000032:analysis / Q000378:metabolism*; D011485:Protein Binding; D014316:Tritium
chemical_list: D002247:Carbon Isotopes; D003470:Culture Media; D004279:DNA, Viral; D010617:Phenanthridines; D014316:Tritium