Architecture et Réactivité de l'ARN, Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire, CNRS, 15 rue René Descartes, 67084 Strasbourg, France.
FEBS Lett. 2014 Aug 1;588(15):2464-9. doi: 10.1016/j.febslet.2014.06.031. Epub 2014 Jun 17.
The natural bases of nucleic acids form a great variety of base pairs with at least two hydrogen bonds between them. They are classified in twelve main families, with the Watson-Crick family being one of them. In a given family, some of the base pairs are isosteric between them, meaning that the positions and the distances between the C1' carbon atoms are very similar. The isostericity of Watson-Crick pairs between the complementary bases forms the basis of RNA helices and of the resulting RNA secondary structure. Several defined suites of non-Watson-Crick base pairs assemble into RNA modules that form recurrent, rather regular, building blocks of the tertiary architecture of folded RNAs. RNA modules are intrinsic to RNA architecture are therefore disconnected from a biological function specifically attached to a RNA sequence. RNA modules occur in all kingdoms of life and in structured RNAs with diverse functions. Because of chemical and geometrical constraints, isostericity between non-Watson-Crick pairs is restricted and this leads to higher sequence conservation in RNA modules with, consequently, greater difficulties in extracting 3D information from sequence analysis. Nucleic acid helices have to be recognised in several biological processes like replication or translational decoding. In polymerases and the ribosomal decoding site, the recognition occurs on the minor groove sides of the helical fragments. With the use of alternative conformations, protonated or tautomeric forms of the bases, some base pairs with Watson-Crick-like geometries can form and be stabilized. Several of these pairs with Watson-Crick-like geometries extend the concept of isostericity beyond the number of isosteric pairs formed between complementary bases. These observations set therefore limits and constraints to geometric selection in molecular recognition of complementary Watson-Crick pairs for fidelity in replication and translation processes.
核酸的天然碱基形成了各种各样的碱基对，它们之间至少有两个氢键。它们被分为十二个主要家族，其中包括 Watson-Crick 家族。在给定的家族中，一些碱基对之间是等排的，这意味着 C1'碳原子的位置和距离非常相似。互补碱基之间 Watson-Crick 碱基对的等排性构成了 RNA 螺旋和由此产生的 RNA 二级结构的基础。一些定义明确的非 Watson-Crick 碱基对套件组装成 RNA 模块，这些模块形成折叠 RNA 三级结构的反复出现的、相当规则的构建块。RNA 模块是 RNA 结构的固有组成部分，因此与特定于 RNA 序列的生物功能无关。RNA 模块存在于所有生命领域和具有多种功能的结构化 RNA 中。由于化学和几何限制，非 Watson-Crick 碱基对之间的等排性受到限制，这导致 RNA 模块中的序列保守性更高，因此从序列分析中提取 3D 信息的难度更大。核酸螺旋必须在复制或翻译解码等几个生物过程中被识别。在聚合酶和核糖体解码位点，识别发生在螺旋片段的小沟侧。通过使用替代构象、质子化或互变异构形式的碱基，可以形成并稳定一些具有 Watson-Crick 样几何形状的碱基对。这些具有 Watson-Crick 样几何形状的碱基对中的一些扩展了等排性的概念，超出了互补碱基之间形成的等排碱基对的数量。这些观察结果为复制和翻译过程中互补 Watson-Crick 对的分子识别中的几何选择设定了限制和约束条件，以确保保真度。
