Open AccessThe B↔Z transition of poly(dI-br5dC).poly(dI-br5dC). A quantitative description of the Z form dynamic structure
Author(s) -
Brigitte Hartmann,
J. Pilet,
Marius Ptak,
Jean Ramstein,
Bernard Malfoy,
Marc Leng
Publication year - 1982
Publication title -
nucleic acids research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 9.008
H-Index - 537
eISSN - 1362-4954
pISSN - 0305-1048
DOI - 10.1093/nar/10.10.3261
Subject(s) - polynucleotide , absorbance , circular dichroism , crystallography , hydrogen bond , z dna , absorption (acoustics) , analytical chemistry (journal) , nuclear magnetic resonance , stereochemistry , chemistry , molecule , materials science , physics , dna , biochemistry , organic chemistry , chromatography , composite material
The study of poly(dI-br5dC).poly(dI-br5dC) films by infrared spectroscopy shows that in low salt concentration, the conformation of this polynucleotide belongs to the B-family and in high salt concentration to the Z-family. 31P nuclear magnetic resonance and circular dichroism confirm the existence of these two forms. By circular dichroism and ultraviolet absorption, it is shown that the equilibrium constant of the B reversible Z transition depends upon temperature. The deuteration rates of exchangeable protons involved in hydrogen bonds between base pairs were deduced from the changes in absorbance near 1700 cm-1. In the B-form, one class of protons is measured with an exchange half-time of 20 minutes. In the Z-form, two classes of protons are measured with very different exchange half-times, the exchange half-time of the slow protons being of the order of 850 minutes. By comparison of these results with those previously obtained for poly(dG-dC).poly(dG-dC), these very slow protons of these two Z-polynucleotides are identified as the cytosine amino protons. A quantitative description of the dynamic structure of the Z-form is presented.