Petraccone Luigi
Dipartimento di Scienze Chimiche, Università degli Studi di Napoli "Federico II", Via Cintia, 80126, Napoli, Italy,
Top Curr Chem. 2013;330:23-46. doi: 10.1007/128_2012_350.
Structural studies have shown that four G-tracts along a DNA strand are the minimal requirement for intramolecular G-quadruplex formation. Longer DNA sequences containing multiples of four G-tracts could, in principle, form higher-order structures based on multiple G-quadruplex blocks. This latter condition is abundantly verified for the telomeric single-stranded overhang (~200 nt) consisting of tens of TTAGGG repeats, thus opening new interesting questions about the structure of the "real" telomeric DNA. How many quadruplex units form in the human telomeric overhang? Which type of quadruplex topologies? Do they interact or not? What about their binding properties? Although many of these questions are still unanswered, recent experimental and computational studies have begun to address them. The existence and relevance of these higher-order quadruplex structures in the human genome is now an interesting and stimulating research topic in the quadruplex field. The recent results, the unsolved problems, and the future prospects for understanding higher-order telomeric quadruplex structures are the main topics of this review. Other studies on long telomeric RNA sequences and on other intramolecular (non telomeric) DNA higher order quadruplex structures are also presented.
结构研究表明，沿着DNA链的四个G序列是分子内G-四链体形成的最低要求。原则上，包含四个G序列倍数的更长DNA序列可以基于多个G-四链体模块形成更高阶的结构。对于由数十个TTAGGG重复序列组成的端粒单链悬垂（约200个核苷酸），后一种情况得到了充分验证，从而开启了关于“真实”端粒DNA结构的新的有趣问题。人类端粒悬垂中形成了多少个四链体单元？哪种类型的四链体拓扑结构？它们是否相互作用？它们的结合特性如何？尽管这些问题中的许多仍然没有答案，但最近的实验和计算研究已经开始解决这些问题。这些高阶四链体结构在人类基因组中的存在和相关性现在是四链体领域一个有趣且具有启发性的研究课题。最近的研究结果、未解决的问题以及理解高阶端粒四链体结构的未来前景是本综述的主要主题。还介绍了关于长端粒RNA序列和其他分子内（非端粒）DNA高阶四链体结构的其他研究。
