Extensive circular dichroism studies have been conducted with the title polynucleotides under various solution conditions. The studies provided the following information: (i) The halogen atoms in place of thymine methyl hinder the isomerization into X-DNA. (ii) The brominated but not iodinated polynucleotide isomerizes into Z-DNA in concentrated NaCl+NiCl2. The transition takes place at lower NiCl2 concentrations than with poly(dA-dT). (iii) The iodinated polynucleotide forms an unusual conformation in aqueous solution in which it is very stable. It isomerizes from this conformer into the usual B-type double helix in concentrated ethanol solutions. The isomerization is a two-state cooperative process. (iv) Both title polynucleotides undergo still another two-state cooperative transition in trifluorethanol solutions presumably into A-DNA showing a rather unusual circular dichroism spectrum.

• MeSH
• Circular Dichroism MeSH
• Idoxuridine chemistry   MeSH
• Nucleic Acid Conformation * MeSH
• Poly A-U chemistry   MeSH
• Poly dA-dT chemistry   MeSH
• Spectrum Analysis MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Idoxuridine MeSH
• poly (dA-BrdU) MeSH Browser
• Poly A-U MeSH
• Poly dA-dT MeSH
• poly(dA-IdU) MeSH Browser

It is shown, using circular dichroism spectroscopy, that poly(dI-dC) is capable to isomerize into both Z-DNA and A-DNA in concentrated NaCl + NiCl2 and trifluoroethanol solutions, respectively. This polynucleotide also undergoes a cooperative, two-state transition in ethanol into a structure which most probably is a canonical B-DNA. This implies that the conformation of poly(dI-dC) is unusual in low-salt aqueous solution. The canonical B-DNA is also adopted by poly(dI-methyl5dC) in trifluoroethanol while this polynucleotide adopts Z-DNA not only in NaCl + NiCl2 but also in the presence of MgCl2. Poly(dI-methyl5dC) partially adopts X-DNA in concentrated CsF and mainly ethanolic solutions. Poly(dI-bromo5dC) isomerizes into Z-DNA not only in concentrated NaCl even in the absence of NiCl2 but also in concentrated MgCl2. This polynucleotide transforms between two distinct variants of Z-DNA in ethanol or trifluoroethanol solutions.

• MeSH
• Magnesium Chloride MeSH
• Sodium Chloride MeSH
• Circular Dichroism MeSH
• DNA chemistry   MeSH
• Isomerism MeSH
• Nucleic Acid Conformation MeSH
• Polydeoxyribonucleotides chemistry   MeSH
• Solutions MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Magnesium Chloride MeSH
• Sodium Chloride MeSH
• DNA MeSH
• poly d(I-C) MeSH Browser
• polydeoxyinosinic-polydeoxy-(5-bromocytidylic)acid MeSH Browser
• polydeoxyinosinic-polydeoxy-(5-methylcytidylic)acid MeSH Browser
• Polydeoxyribonucleotides MeSH
• Solutions MeSH