Nucleic Acids Research

Polymorphic forms of the DNA duplex with long stretches of structural monotony are known. Several alternating purine-pyrimidine sequences have been shown to adopt left-handed Z-conformation. We report a DNA sequence d(CGCGCGATCGAT)n exhibiting alternating right-handed B and lefthanded Z helical conformation after every half a turn. Further, this unusual conformation with change in handedness after every six base pairs was induced at physiological superhelical density.