Patel D J, Canuel L L, Pohl F M
Proc Natl Acad Sci U S A. 1979 Jun;76(6):2508-11. doi: 10.1073/pnas.76.6.2508.
The high resolution 1H and 31P NMR spectra of the (dG-dC)8 duplex have been recorded in low- and high-salt solutions in order to evaluate the structural aspects of the salt-induced transition of oligo(dG-dC) in solution [Pohl, F. M. & Jovin, T. M. (1972) J. Mol. Biol. 67, 375-396]. The NMR data require that the (dG-dC)8 duplex in 4 M NaCl adopt an "alternating B-DNA" conformation for which the symmetry unit repeats every two base pairs. By contrast, the oligomer duplex in low-salt solution is of the regular B-DNA type in solution. The chemical shift parameters for oligo(dG-dC) in high-salt solution demonstrate that every other glycosidic torsion angle and phosphodiester linkage adopts a different conformation from that observed in regular B-DNA. We demonstrate further that the generation of the "alternating B-DNA" structure is facilitated by introduction of halogen atoms at the 5 position of pyrimidine and that this probably reflects the greater overlap of this position with adjacent base pairs in high salt solution. An "alternating B-DNA" model has recently been proposed for alternating deoxy purine-deoxy pyrimidine polynucleotides based on the x-ray structure of pdA-dT-dA-dT [Klug, A., Jack, A., Viswamitra, M.A., Kennard, O., Shakked, Z. & Steitz, T.A. (1979) J. Mol. Biol., in press].
为了评估溶液中寡聚（dG-dC）盐诱导转变的结构方面，已在低盐和高盐溶液中记录了（dG-dC）8双链体的高分辨率1H和31P NMR光谱[Pohl，F.M.和Jovin，T.M.（1972年）《分子生物学杂志》67，375 - 396]。NMR数据表明，在4M NaCl中的（dG-dC）8双链体采用“交替B-DNA”构象，其对称单元每两个碱基对重复一次。相比之下，低盐溶液中的寡聚物双链体在溶液中是规则的B-DNA类型。高盐溶液中寡聚（dG-dC）的化学位移参数表明，每隔一个糖苷扭转角和磷酸二酯键采用与规则B-DNA中观察到的不同的构象。我们进一步证明，在嘧啶的5位引入卤原子有助于“交替B-DNA”结构的产生，这可能反映了该位置在高盐溶液中与相邻碱基对的更大重叠。最近基于pdA-dT-dA-dT的x射线结构[Klug，A.，Jack，A.，Viswamitra，M.A.，Kennard，O.，Shakked，Z.和Steitz，T.A.（1979年）《分子生物学杂志》，即将发表]，针对交替脱氧嘌呤-脱氧嘧啶多核苷酸提出了“交替B-DNA”模型。
