Organic Chemistry Section, Inorganic and Organic Chemistry Department, University of Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain.
Institute of Biomedicine, University of Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain.
Molecules. 2022 Aug 19;27(16):5287. doi: 10.3390/molecules27165287.
Tetrads (or quartets) are arrangements of four nucleobases commonly involved in the stability of four-stranded nucleic acids structures. Four-stranded or quadruplex structures have attracted enormous attention in the last few years, being the most extensively studied guanine quadruplex (G-quadruplex). Consequently, the G-tetrad is the most common and well-known tetrad. However, this is not the only possible arrangement of four nucleobases. A number of tetrads formed by the different nucleobases have been observed in experimental structures. In most cases, these tetrads occur in the context of G-quadruplex structures, either inserted between G-quartets, or as capping elements at the sides of the G-quadruplex core. In other cases, however, non-G tetrads are found in more unusual four stranded structures, such as i-motifs, or different types of peculiar fold-back structures. In this report, we review the diversity of these non-canonical tetrads, and the structural context in which they have been found.
四联体（或四联体）是通常涉及四链核酸结构稳定性的四个碱基的排列。四链或四重结构在过去几年中引起了极大的关注，其中最广泛研究的是鸟嘌呤四联体（G-四联体）。因此，G-四联体是最常见和最知名的四联体。然而，这不是四个碱基的唯一可能排列。在实验结构中已经观察到由不同碱基形成的许多四联体。在大多数情况下，这些四联体出现在 G-四联体结构的上下文中，要么插入 G-四联体之间，要么作为 G-四联体核心两侧的封端元件。然而，在其他情况下，在更不寻常的四链结构中发现了非 G 四联体，例如 i- 基序或不同类型的特殊折返结构。在本报告中，我们回顾了这些非规范四联体的多样性，以及它们被发现的结构背景。
