Bacolla A, Gellibolian R, Shimizu M, Amirhaeri S, Kang S, Ohshima K, Larson J E, Harvey S C, Stollar B D, Wells R D
Center for Genome Research, Institute of Biosciences and Technology, Texas A & M University, Texas Medical Center, 2121 Holcombe Blvd., Houston, Texas 77030, USA.
J Biol Chem. 1997 Jul 4;272(27):16783-92. doi: 10.1074/jbc.272.27.16783.
The properties of duplex CTG.CAG and CGG.CCG, which are involved in the etiology of several hereditary neurodegenerative diseases, were investigated by a variety of methods, including circularization kinetics, apparent helical repeat determination, and polyacrylamide gel electrophoresis. The bending moduli were 1.13 x 10(-19) erg.cm for CTG and 1.27 x 10(-19) erg.cm for CGG, approximately 40% less than for random B-DNA. Also, the persistence lengths of the triplet repeat sequences were approximately 60% the value for random B-DNA. However, the torsional moduli and the helical repeats were 2.3 x 10(-19) erg.cm and 10.4 base pairs (bp)/turn for CTG and 2.4 x 10(-19) erg.cm and 10.3 bp/turn for CGG, respectively, all within the range for random B-DNA. Determination of the apparent helical repeat by the band shift assay indicated that the writhe of the repeats was different from that of random B-DNA. In addition, molecules of 224-245 bp in length (64-71 triplet repeats) were able to form topological isomers upon cyclization. The low bending moduli are consistent with predictions from crystallographic variations in slide, roll, and tilt. No unpaired bases or non-B-DNA structures could be detected by chemical and enzymatic probe analyses, two-dimensional agarose gel electrophoresis, and immunological studies. Hence, CTG and CGG are more flexible and highly writhed than random B-DNA and thus would be expected to act as sinks for the accumulation of superhelical density.
通过多种方法研究了与几种遗传性神经退行性疾病病因相关的双链CTG.CAG和CGG.CCG的特性，这些方法包括环化动力学、表观螺旋重复序列测定和聚丙烯酰胺凝胶电泳。CTG的弯曲模量为1.13×10⁻¹⁹尔格·厘米，CGG的弯曲模量为1.27×10⁻¹⁹尔格·厘米，比随机B-DNA的弯曲模量约低40%。此外，三联体重复序列的持久长度约为随机B-DNA值的60%。然而，CTG的扭转模量和螺旋重复序列分别为2.3×10⁻¹⁹尔格·厘米和10.4碱基对/圈，CGG的扭转模量和螺旋重复序列分别为2.4×10⁻¹⁹尔格·厘米和10.3碱基对/圈，均在随机B-DNA的范围内。通过带移分析测定表观螺旋重复序列表明，重复序列的扭曲与随机B-DNA的扭曲不同。此外，长度为224 - 245碱基对（64 - 71个三联体重复）的分子在环化时能够形成拓扑异构体。低弯曲模量与滑动、滚动和倾斜的晶体学变化预测一致。通过化学和酶促探针分析、二维琼脂糖凝胶电泳和免疫学研究未检测到未配对碱基或非B-DNA结构。因此，CTG和CGG比随机B-DNA更具柔韧性且高度扭曲，因此预计它们会作为超螺旋密度积累的汇聚点。
