Up to now, the left-handed, double-helical DNA was found only in crystals and in solutions of oligo- and polynucleotides of the alternating d(C-G) sequences under high salt concentration, such as 2.5 m NaCl or 0.7 m MgCl2 (Pohl and Jovin 1972; Wang et al. 1979, 1981; Drew et al. 1980; Drew and Dickerson 1981; Klysik et al. 1981). Methylation of the cytidine residues of this d(C-G) sequence lowers the salt concentration necessary for the B→Z transition (Bene and Felsenfeld 1981). However, the presence of such Z forms in vivo limited only to alternating d(C-G) sequences is unlikely. It was thus of interest to investigate whether DNA with natural base sequences will form a stable left-handed, double-helical conformation under conditions of low salt concentration close to physiological. We investigated the conformation of form-V DNA, which is obtained by reassociation of complementary, circular single strands as described by Stettler et al. (1979)...
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Brahms et al. (1983) studied this question.