Conformational Transitions of Poly(dl-dC) in Aqueous Solution as Studied by Ultraviolet Resonance Raman Spectroscopy |
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Authors: | Pavol Miskovsky Alena Tomkova Laurent Chinsky Pierre-Yves Turpin |
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Affiliation: | 1. Department of Biophysics , Safarik University , 04154 , Kosice , Slovakia;2. L.P.C.B. (CNRS UA 198) Institut Curie and Université P. et M. Curie , 11, rue P. &3. M. Curie, 75231 , Paris Cedex 05 , France |
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Abstract: | Abstract Poly(dI-dC) in aqueous solution can undergo different equilibrium geometries, which strongly depend on salt nature and concentrations. These equilibrium structures have been monitored by resonance Raman spectroscopy (RRS) measurements in the ultraviolet region, i. e. by using 257 and 281 nm laser excitation wavelengths which favor the resonance enhancement of the Raman contributions from inosine and cytosine residues of poly(dI-dC), respectively. Spectral changes depending on the NaCl concentration and on the presence of Ni2+ ions have been observed and interpreted in comparison with RRS results previously obtained for other alternating purine-pyrimidine polydeoxyribonucleotides, i.e. poly(dG-dC), poly(dA- dT) and poly(dA-dC). poly(dG-dT), which also showed B to Z conformational transitions in varying the salt concentrations. It is shown here that: i) the base stacking geometries are nearly the same in the high-salt form (5 M NaCl) of poly(dl-dC) as in the low-salt form (0.1M NaCl) of the polymer, ii) however, the high-salt structure yields important differences from a B-helix (obtained in low-salt solution) as regards the nucleoside conformations (sugar puckering and base-sugar orientation), and: iii) the addition of 9 mM NiCl2 in the high-salt (5 M NaCl) solution of poly(dI-dC) induces the Z-conformation of the polymer. |
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