Generation of Left-handed Z-DNA in Solution and Visualization

The prototype for left-handed, double-helical DNA in solution is provided by the synthetic polynucleotide poly[d(G-C)] exposed to high concentrations (> 2.5 M) of NaCI (Pohl and Jovin 1972). However, numerous crystallographic and other studies documented in this volume and elsewhere have established the polymorphic nature of the Z family of left-handed conformations and delineated the numerous factors that can greatly enhance the probability of the B--Z transition: (1) increased ionic strength; (2) decreased water activity; (3) site-specific interactions ofcations and anions; (4) increased temperature; (5) increased negative superhelical densi-ty; (6) binding of peptides and proteins, including polyamines, antibodies, and core histones (Miller et al., this volume); and (7) chemical modification of the DN