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DNA polymorphism: Spectroscopic and electro‐optic characterizations of Z‐DNA and other types of left‐handed helical structures induced by Ni 2+
Author(s) -
Hacques MarieFrançoise,
Marion Christian
Publication year - 1986
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360251206
Subject(s) - chemistry , polynucleotide , birefringence , crystallography , dipole , circular dichroism , stereochemistry , biochemistry , physics , organic chemistry , quantum mechanics
CD and uv spectroscopy reveal that the synthetic polynucleotides poly(dG–dC) · poly(dG–dC) and poly(dG–m 5 dC) · poly(dG–m 5 dC) undergo a transition induced by small amounts of Ni ++ cation from a right‐handed B‐form to left‐handed Z‐type conformations. We describe the application of steady‐state and transient electric birefringence to the characterization of the transition observed at very low ionic strength (10 m M Tris HCl, pH 7.4). Dialysis experiments show that the changes in spectroscopic and electro‐optic properties upon addition of Ni ++ are completely reversible. The differences in shape of the inverted CD spectra suggest the existence of a family of left‐handed conformations, depending on the polymer used and on the amounts of cation added. The stoichiometry required for inducing the Z‐conformation of poly(dG–m 5 dC) is 1 cation/4 nucleotide phosphates. The transition is accompanied by a decrease in birefringence, an increase in length, and the more important contribution of a permanent or slowly induced dipole moment to the orientation mechanism. High concentrations of Ni ++ promote the Z → Z* transition. Upon increasing the Ni ++ concentration, poly(dG–dC) undergoes a biphasic transition, first to one intermediate conformation that is neither B‐ nor Z‐like and then to a left‐handed form that is probably different from Z*. These conversions are accompanied by regular decreases both in birefringence and in chain length, but no transient appears in the field‐reversal experiments.