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Temperature‐dependent conformational transitions in poly(dG‐dC) and poly(dG‐m 5 dC)
Author(s) -
Behe Michael J.,
Felsenfeld Gary,
Szu Shousun Chen,
Charney Elliot
Publication year - 1985
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.360240202
Subject(s) - chemistry , ion , ionic strength , divalent , salt (chemistry) , ionic bonding , solvent , melting temperature , transition temperature , crystallography , organic chemistry , aqueous solution , condensed matter physics , physics , materials science , composite material , superconductivity
The double‐stranded helical complexes of poly(dG‐dC) and of poly(dG‐m 5 dC) are shown to convert from B‐ to Z‐DNA‐type conformations at moderate or low ionic strengths, lower for the 5‐methyl than for the non‐methyl species, in a highly cooperative temperature‐dependent equilibrium. In the presence of low concentrations of divalent ion, e.g., Mg 2+ , the temperature at which the B → Z transition occurs is virtually independent of the salt concentration and the B‐conformation is favored at lower temperature, while the Z‐conformation is favored at higher temperature. Since the Debye‐Hückel screening parameter changes rapidly with ionic strength in this region, electrostatic interaction with the free ions appears to be only a small factor in the forces that promote the transition; the temperature dependence must derive principally from effects on the solvent. The temperature dependence at high salt concentrations is also reported.