Formation of Z-DNA in negatively supercoiled plasmids is sensitive to small changes in salt concentration within the physiological range.
Negative supercoiling of the plasmid pBR322 with or without an insert of (dG-dC)n induces the formation of Z-DNA as measured by the binding of antibodies specific for Z-DNA. Increasing the concentration of Na+ (or K+) is shown to inhibit the B to Z-DNA conversion. This may be due to the effect of the cation on the B-Z junction. Using the data for B to Z-DNA conversion of the (dG-dC)n inserts, we have estimated the free energy change per base pair as well as the energy of the B-Z junction. In pBR322, a 14-bp segment [CACGGGTGCGCATG] is believed to form Z-DNA at bacterial negative superhelical densities under salt conditions which are similar to those found in vivo.
D004247:DNA / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004278:DNA, Superhelical / Q000378:metabolism; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration; D010957:Plasmids; D012965:Sodium Chloride / Q000494:pharmacology
D004278:DNA, Superhelical; D012965:Sodium Chloride; D004247:DNA; D004264:DNA Topoisomerases, Type I