Harder M E, Johnson W C
Department of Biochemistry and Biophysics, Oregon State University, Corvallis 97331-6503.
Nucleic Acids Res. 1990 Apr 25;18(8):2141-8. doi: 10.1093/nar/18.8.2141.
Both multivalent ions and 85% ethanol are required to produce the original Z' form of poly(dGdC):poly(dGdC) in solution. When multivalent impurities are removed by dialysis against 0.5 M NaCl and 1 mM EDTA, the circular dichroism retains features of the standard Z form. Addition of Ca+2 nearly reverses this effect. Analysis by singular value decomposition of near-ultraviolet circular dichroism spectra collected during titrations of polynucleotide in 60% ethanol with multivalent ions reveal that, at concentrations below .5 per nucleotide, they stabilize Z'-like forms in a two-state equilibrium with the Z form. Differences among the Z' spectra produced by the different ions suggest that at least three families of Z' structures exist. Furthermore, comparison with crystal data indicates that the Z' form in solution is related to the ZII form in crystals.
溶液中生成原始的聚（dGdC）:聚（dGdC）Z' 形式需要多价离子和85% 的乙醇。当通过用0.5 M NaCl和1 mM EDTA透析去除多价杂质时，圆二色性保留标准Z形式的特征。添加Ca+2几乎可以逆转这种效应。在用多价离子滴定60% 乙醇中的多核苷酸过程中收集的近紫外圆二色性光谱的奇异值分解分析表明，在每个核苷酸低于0.5 的浓度下，它们在与Z形式的双态平衡中稳定类似Z' 的形式。不同离子产生的Z' 光谱之间的差异表明至少存在三类Z' 结构。此外，与晶体数据的比较表明溶液中的Z' 形式与晶体中的ZII形式有关。
