Left-handed Z-DNA is induced by supercoiling in physiological ionic conditions

Abstract
In physiological ionic conditions (200mM NaCl), the (dC–dG)16 and (dC–dG)13 blocks in plasmid pRW751 are in a left-handed state when the negative superhelical density of the plasmid is greater than 0.072. As the salt concentration decreases or when (dmC–dG) sequences are present, less negative supercoiling is required to induce the right- to left-handed DNA transition. Furthermore, the single strand-specific nuclease, S1, recognizes and cleaves aberrant structural features at the junction between neighbouring right- and left-handed DNA regions.