Protonated polynucleotides structures - 22.CD study of the acid-base titration of poly(dG).poly(dC) (original) (raw)

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Service de Biophysique Départment de Biologie, Centre d'Etudes Nucléaires de Saclay

91190 Gif-sur-Yvette, France

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Service de Biochimie Départment de Biologie, Centre d'Etudes Nucléaires de Saclay

91190 Gif-sur-Yvette, France

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Service de Biophysique Départment de Biologie, Centre d'Etudes Nucléaires de Saclay

91190 Gif-sur-Yvette, France

Search for other works by this author on:

SS

Service de Biochimie Départment de Biologie, Centre d'Etudes Nucléaires de Saclay

91190 Gif-sur-Yvette, France

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Christian Marck, Danielle Thiele, Christian Schneider, Wilhelm Guschlbauer, Protonated polynucleotides structures - 22.CD study of the acid-base titration of poly(dG).poly(dC), Nucleic Acids Research, Volume 5, Issue 6, 1 June 1978, Pages 1979–1996, https://doi.org/10.1093/nar/5.6.1979
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Abstract

The acid-base titration (pH 8 → pH 2.5 → pH 8) of eleven mixing curve samples of the poly(dG) plus poly(dC) system has been performed in 0.15 M NaCl. Upon protonation, poly(dG).poly(dC) gives rise to an acid complex, in various amounts according to the origin of the sample. We have established that the hysteresis of the acid-base titration is due to the non-reversible formation of an acid complex, and the liberation of the homopolymers at the end of the acid titration and during the base titration; the homopolymer mixtures remain stable up to pH 7. A 1G:1C stoichiometry appears to be the most probable for the acid complex, a 1G:2C stoichiometry, as found in poly(C $ ).poly(I).poly(C) or poly(C $ ).poly(G).poly(C), cannot be rejected. In the course of this study, evidence has been found that the structural consequences of protonation could be similar for both double stranded poly(dG).poly(dc)and G-C rich DNA's: 1) protonation starts near pH 6, dissociation of the acid complex of poly(dG).poly(dC) and of protonated DNA take place at pH 3; 2) the CD spectrum computed for the acid polymer complex displays a positive peak at 255 nm as found in the acid spectra of DNA's; 3) double stranded poly(dG).poly(dC) embedded in triple-stranded poly(dG).poly(dG).poly(dC) should be in the A-form and appears to be prevented from the proton induced conformational change. The neutral triple stranded poly(dG).poly(dG).poly(dC) appears therefore responsible, although indirectly, for the complexity and variability of the acid titration of poly(dG).poly(dC) samples.

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