Open AccessStructural changes in positively and negatively supercoiled DNA
Author(s) -
BRAHMS Sabine,
NAKASU Syo,
KIKUCHI Aki,
BRAHMS J. Georges
Publication year - 1989
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1989.tb15019.x
Subject(s) - writhe , dna supercoil , twist , circular dna , dna , linking number , cccdna , crystallography , physics , chemistry , dna replication , mathematics , geometry , gene , biochemistry , genome
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 σ¯). At low and moderate negative superhelical densities σ¯, 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.