Ross P D, Howard F B, Lewis M S
Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892.
Biochemistry. 1991 Jun 25;30(25):6269-75. doi: 10.1021/bi00239a027.
Five highly palindromic DNA dodecamers, four of which may form G-A or I-A purine-purine mispairs at either the 5.8 or 6.7 positions, have been studied at sedimentation equilibrium in the analytical ultracentrifuge. Each DNA oligonucleotide forms an equilibrium mixture of ordered antiparallel hairpin and double-stranded helical structures in solutions of 0.1 or 0.5 M NaCl between 5 and 40 degrees C. The dimeric duplex is favored by conditions of high salt and low temperature. The monomer-dimer equilibrium constants vary from 5 x 10(6) to 5 x 10(3) and are unique for each DNA dodecamer. Analysis of the temperature dependence of the equilibrium constants shows that the double helix to hairpin conversion is driven by a positive entropy change and is associated with an endothermic enthalpy change. The mispair substitutions at the 5.8 positions and the IA(6.7) mispair have the greatest tendency toward hairpin formation and exhibit significantly larger entropy changes than the nonmispaired dGGTACGCGTACC parent sequence and the thermodynamically similar GA(6.7) DNA. The consequences of such hairpin-double helix equilibria must be considered in the interpretation of other kinds of experiments carried out on oligonucleotides at different concentrations.
研究人员利用分析型超速离心机，在沉降平衡条件下对五条高度回文的DNA十二聚体进行了研究，其中四条在5.8或6.7位置可能形成G-A或I-A嘌呤-嘌呤错配。在5至40摄氏度的0.1或0.5 M NaCl溶液中，每条DNA寡核苷酸都形成了有序的反平行发夹结构和双链螺旋结构的平衡混合物。高盐和低温条件有利于二聚体双链体的形成。单体-二聚体平衡常数在5×10⁶至5×10³之间变化，且每条DNA十二聚体的平衡常数都是独特的。对平衡常数的温度依赖性分析表明，从双螺旋到发夹的转变是由正熵变驱动的，并且伴随着吸热焓变。5.8位置的错配取代和IA(6.7)错配形成发夹的倾向最大，并且与未错配的dGGTACGCGTACC亲本序列以及热力学上相似的GA(6.7) DNA相比，表现出明显更大的熵变。在解释对不同浓度寡核苷酸进行的其他类型实验时，必须考虑这种发夹-双螺旋平衡的影响。
