title: Structural changes in positively and negatively supercoiled DNA.
abstract: The effect of superhelical constraint on the structure of covalently closed circular DNA (cccDNA; pBR322) with positive and negative writhe (superturn) has been investigated as a function of decreasing and increasing specific linking difference (mean superhelical density sigma). At low and moderate negative superhelical densities sigma, the overall average structure is maintained in an unwound B-form slightly modified. The overwound cccDNAs with positive writhe differ from those with negative writhe by an absence of cruciform structure. At high negative densities of supercoiling different changes involving the reversal of twist handedness are shown to lead to the formation of DNA segments in a conformation identical to the left-handed component of form V DNA.
authors: Institut Jacques Monod, Centre National de la Recherche Scientifique, Université Paris VII, France.
authors: S
authors: S
authors: Brahms
authors: S
authors: S
authors: Nakasu
authors: A
authors: A
authors: Kikuchi
authors: J G
authors: JG
authors: Brahms
mesh_terms: D002942:Circular Dichroism; D004278:DNA, Superhelical / Q000302:isolation & purification / Q000648:ultrastructure; D003850:Deoxyribonuclease I; D015180:Electrophoresis, Gel, Two-Dimensional; D007536:Isomerism; D009690:Nucleic Acid Conformation; D010957:Plasmids; D015183:Restriction Mapping; D013059:Spectrum Analysis, Raman
chemical_list: D004278:DNA, Superhelical; D003850:Deoxyribonuclease I