Efforts to expand the genetic alphabet are predicated upon a stable and replicable third base pair. Recent progress has resulted in the development of several candidates that are both stable in duplex DNA and replicated by DNA polymerases with various degrees of efficiency and fidelity. The candidate base pairs draw upon unnatural hydrogen-bonding topologies as well as upon shape complementarity and hydrophobic forces. This review provides a critical comparison of the third base pair candidates and discusses the further work required to expand the genetic alphabet.

中文翻译：

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超越A，C，G和T：增加自然界的字母。

扩展遗传字母的努力基于稳定且可复制的第三碱基对。最近的进展导致开发了几种候选物，这些候选物在双链体DNA中都稳定，并且可以通过DNA聚合酶以不同的效率和保真度复制。候选碱基对利用不自然的氢键拓扑结构，形状互补性和疏水力。这篇综述提供了第三碱基对候选者的关键比较，并讨论了扩展遗传字母所需的进一步工作。