Structural forms, stabilities and transitions in double-helical poly(dG-dC) as a function of hydration and NaCl content. An infrared spectroscopic study.
The poly(dG-dC) helical duplex forms a modified, B-family 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 NaCl content stabilizes B* with respect to B. Poly(dG-dC) forms the Z structure at low NaCl contents when the hydration is sufficiently reduced. At moderate NaCl 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 structure 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.
D004247:DNA; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides; D012965:Sodium Chloride; D013055:Spectrophotometry, Infrared; D014867:Water
D011089:Polydeoxyribonucleotides; D014867:Water; C019530:poly(dC-dG); D012965:Sodium Chloride; D004247:DNA