Sen D, Gilbert W
Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138.
Biochemistry. 1992 Jan 14;31(1):65-70. doi: 10.1021/bi00116a011.
DNA oligomers containing three or more contiguous guanines form tetrastranded parallel complexes, G4-DNA, in the presence of alkali cations. However, oligomers that have a single multi-guanine motif at their 3' or 5' end, with a guanine as the terminal base, also form higher order products. Thus, the oligomer T8G3T forms a unique G4-DNA product at neutral pH in the presence of Na+, K+, or Rb+; however, its isomeric counterpart T9G3 in K+ or Rb+ generates an additional ladder of products of substantially lower gel mobility. We show that these larger complexes contain, respectively, 8, 12, or 16 distinct strands of oligomer. The octamer structure formed by T9G3 assembles in moderate salt at room temperature and melts around 60 degrees C in 100 mM KCl. Methylation protection experiments suggest a nested head-to-tail superstructure containing two tetraplexes bonded front-to-back via G quartets formed by out-of-register guanines. Naturally occurring chromosomal telomeres, which all have guanines at their 3' termini, may be able to form these superstructures.
在碱金属阳离子存在的情况下，含有三个或更多连续鸟嘌呤的DNA寡聚物会形成四链平行复合物，即G4-DNA。然而，在其3'或5'末端具有单个多鸟嘌呤基序且以鸟嘌呤作为末端碱基的寡聚物，也会形成高阶产物。因此，寡聚物T8G3T在中性pH条件下，于Na+、K+或Rb+存在时会形成独特的G4-DNA产物；然而，其异构体T9G3在K+或Rb+中会产生另外一系列凝胶迁移率显著更低的产物。我们表明，这些更大的复合物分别包含8条、12条或16条不同的寡聚物链。由T9G3形成的八聚体结构在室温下的中等盐浓度中组装，并在100 mM KCl中于约60摄氏度时解链。甲基化保护实验表明存在一种嵌套的头对头超结构，其中包含两个通过由错位鸟嘌呤形成的G四联体前后相连的四链体。天然存在的染色体端粒在其3'末端均含有鸟嘌呤，可能能够形成这些超结构。
