The A--B transition: temperature and base composition effects on hydration of DNA.
Natural DNAs and some polynucleotides organised in fiber present the A--B form transition at a relative humidity (r.h.) which depends on the temperature. A shift of the midpoint of that helix--helix transition to higher r.h. values is observed when the temperature is risen. It is shown that the average number of water molecules associated to a nucleotide pair is the relevant parameter for the A-B transition and that this parameter can be given a precise value by a combination of different r.h. and temperature values. The minimum number of water molecules necessary to get the B form depends on the base composition of the DNA. It is observed that AT base pairs have a higher affinity toward water molecules than GC base pairs. In the B form there are 27 water molecules per GC nucleotide pair and 44 per AT pair. Moreover, we noted that the fraction of nucleotides in the B form as a function of the average number of water molecules associated per base pair does not depend on the temperature. The A helical form is obtained with about 11 water molecules per nucleotide pair and this number is not very sensitive to the base composition of DNA.
Albiser
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Laboratoire de Biophysique Moleculaire, UMR 7565 Universite H. Poincare, Faculte des Sciences, BP 239, 54506, Vandoeuvre les Nancy, France.
Lamiri
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A
Premilat
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D020029:Base Pairing; D004247:DNA / Q000737:chemistry*; D011119:Polynucleotides / Q000737:chemistry; D012964:Sodium / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D014867:Water; D014961:X-Ray Diffraction
D011119:Polynucleotides; D014867:Water; D004247:DNA; D012964:Sodium