Date of Original Version
The poly(dG-dC) helical duplex forms a modified, B-familoy structure (B*) at very high hydration and a normal B structure at slightly lower hydration. The B* structure is slightly different in sugar-phosphate and base-stacking conformations than the B structure. Increasing the hydration or decreasing the NaC1 content stabilizes B* with respect to B.
Poly(dG-dC) forms the Z structure at low NaC1 contents when the hydration is sufficiently reduced. At moderate NaC1 content, the B to Z transition is sharp and cooperative for hydration with D2O. Hydration with H2O broadens the transition which occurs at lower hydration. This suggests that hydrogen bonding is stronger in the Z structute and helps stabilize Z over B.
IR spectra may be used to quantitatively estimate the fractions of B and Z structures present in a sample. Some new indicator bands are described.
P. B. Keller, K. A. Hartman; Structural forms, stabilities and transitions in double-helical poly(dG-dC) as a function of hydration and NaCI content. An infrared spectroscopic study, Nucleic Acids Research, Volume 14, Issue 20, 1 October 1986, Pages 8167–8182, https://doi.org/10.1093/nar/14.20.8167
Available at: http://dx.doi.org/10.1093/nar/14.20.8167