Shchyolkina A K, Borisova O F, Chernov B K, Tchurikov N A
V.A. Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow.
J Biomol Struct Dyn. 1994 Jun;11(6):1237-49. doi: 10.1080/07391102.1994.10508066.
Parallel-stranded deoxyoligonucleotide 5'd(CTATAGGGAT)3'/5'd(GATATCCCTA)3' (I-II) was shown to be stable in solution at 3 degrees-5 degrees C, 0.1-0.25 M NaCl, 10(-2) M phosphate buffer, pH 7.0 by means of a set of fluorescent techniques as well as of conventional optical methods. A cooperative change in the CD spectra is observed in trifluoroethanol (TFE) solutions at decreased water activity (relative humidity, r.h.). This distinctive change is supposed to stem from a cooperative conformational transition of parallel double helix from a B-like form with C2' endo sugar conformation to an A-like form designated as Ap. The free energy difference between the Ap and B-like conformation for the parallel duplex is 7.35 kcal/mol which is close to the value 7.40 kcal/mol for the antiparallel 5'd(CTATAGGGAT)3'/3'd(GATATCCCTA)5' (I-III). The ability of parallel helix to transit into Ap form is important for DNA-RNA parallel double helix formation.
通过一系列荧光技术以及传统光学方法表明，平行链脱氧寡核苷酸5'd(CTATAGGGAT)3'/5'd(GATATCCCTA)3'（I-II）在3℃-5℃、0.1-0.25M NaCl、10⁻²M磷酸盐缓冲液（pH 7.0）的溶液中是稳定的。在水活性降低（相对湿度，r.h.）的三氟乙醇（TFE）溶液中，观察到圆二色光谱（CD光谱）的协同变化。这种独特的变化被认为源于平行双螺旋从具有C2'内型糖构象的B样形式到指定为Ap的A样形式的协同构象转变。平行双链体的Ap构象和B样构象之间的自由能差为7.35千卡/摩尔，这与反平行的5'd(CTATAGGGAT)3'/3'd(GATATCCCTA)5'（I-III）的7.40千卡/摩尔的值接近。平行螺旋转变为Ap形式的能力对于DNA-RNA平行双螺旋的形成很重要。
