Conformational transitions of poly(dA-dC).poly(dG-dT), poly(dA-dT).poly(dA-dT), and other alternating purine-pyrimidine DNAs were studied in aqueous ethanol solutions containing molar concentrations of sodium perchlorate, which is a novel solvent stabilizing non-B duplexes of DNA. Using CD and UV absorption spectroscopies, we show that this solvent unstacks bases and unwinds the B-forms of the DNAs to transform them into the A-form or Z-form. In the absence of divalent cations poly(dA-dC).poly(dG-dT) can adopt both of these conformations. Its transition into the Z-form is induced at higher salt and lower ethanol concentrations, and at higher temperatures than the transition into the A-form. Submillimolar concentrations of NiCl2 induce a highly cooperative and slow A-Z transition or Z-Z' transition, which is fast and displays low cooperativity. Poly(dA-dT).poly(dA-dT) easily isomerizes into the A-form in perchlorate-ethanol solutions, whereas high perchlorate concentrations denature the polynucleotide, which then cannot adopt the Z-form. At low temperatures, however, NiCl2 also cooperatively induces the Z'-form in poly(dA-dT).poly(dA-dT). Poly(dI-dC).poly(dI-dC) is known to adopt an unusual B-form in low-salt aqueous solution, which is transformed into a standard B-form by the combination of perchlorate and ethanol. NiCl2 then transforms poly(dI-dC).poly(dI-dC) into the Z'-form, which is also adopted by poly(dI-br5dC).poly(dI-br5dC).

• MeSH
• Biophysics MeSH
• Biophysical Phenomena MeSH
• Circular Dichroism MeSH
• Nucleic Acid Denaturation MeSH
• DNA chemistry   MeSH
• Ethanol MeSH
• Nucleic Acid Conformation * MeSH
• Perchlorates MeSH
• Poly dA-dT chemistry   MeSH
• Polydeoxyribonucleotides chemistry   MeSH
• Solutions MeSH
• Base Sequence MeSH
• Sodium Compounds MeSH
• Spectrophotometry, Ultraviolet MeSH
• In Vitro Techniques MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA MeSH
• Ethanol MeSH
• Perchlorates MeSH
• Poly dA-dT MeSH
• poly(d(G-T).d(C-A)) MeSH Browser
• Polydeoxyribonucleotides MeSH
• Solutions MeSH
• Sodium Compounds MeSH
• sodium perchlorate MeSH Browser