Benight A S, Wang Y S, Amaratunga M, Chattopadhyaya R, Henderson J, Hanlon S, Ikuta S
Department of Chemistry, University of Illinois, Chicago 60680.
Biochemistry. 1989 Apr 18;28(8):3323-32. doi: 10.1021/bi00434a030.
The physical properties of the DNA oligomer d(CGCGCGTTTTCGCGCG) in solvents containing 4 M NaClO4 and 0.1 M NaCl were investigated by proton NMR, optical melting, and circular dichroism spectroscopy. Results of these investigations are as follows: (i) The DNA hexadecamer exists as a unimolecular hairpin in either high or low salt. (ii) In high salt the stem region of the hairpin is in the left-handed Z conformation. (iii) In either high or low salt, the duplex stem of the hairpin is stabilized against melting by approximately 40 degrees C compared to the linear core duplex. The added stability of the hairpin is entropic in origin. (iv) In high salt, as the temperature is elevated, the equilibrium structure of the duplex stem of the hairpin shifts from the Z to the B conformation before melting. (v) In low salt, when the DNA duplex exists in the B conformation, attachment of a T4 single-strand loop to one end only slightly decreases (by 14%) the correlation time of the CH5-CH6 interproton vector. In high salt, when the DNA duplex exists in the Z conformation, the correlation time of the CH5-CH6 interproton vector decreases by 51%. Since these viscosity-corrected correlation times are taken to be indicators of duplex motions on the nanosecond time scale, this result directly suggests a larger amplitude of these motions is present in the duplex stem of the hairpin when it exists in the Z conformation.
通过质子核磁共振、光学熔解和圆二色光谱法研究了DNA寡聚物d(CGCGCGTTTTCGCGCG)在含有4 M高氯酸钠和0.1 M氯化钠的溶剂中的物理性质。这些研究结果如下：(i) DNA十六聚体在高盐或低盐条件下均以单分子发夹形式存在。(ii) 在高盐条件下，发夹的茎区呈左手Z构象。(iii) 在高盐或低盐条件下，与线性核心双链体相比，发夹的双链茎对熔解的稳定性提高了约40摄氏度。发夹增加的稳定性源于熵。(iv) 在高盐条件下，随着温度升高，发夹双链茎的平衡结构在熔解前从Z构象转变为B构象。(v) 在低盐条件下，当DNA双链体呈B构象时，仅在一端连接T4单链环只会使CH5-CH6质子间向量的相关时间略有降低(降低14%)。在高盐条件下，当DNA双链体呈Z构象时，CH5-CH6质子间向量的相关时间降低51%。由于这些经过粘度校正的相关时间被视为纳秒时间尺度上双链运动的指标，这一结果直接表明，当发夹的双链茎呈Z构象时，其双链运动的幅度更大。
