The chemical replication of RNA inside fatty acid vesicles is a plausible step in the emergence of cellular life. On the primitive Earth, simple protocells with the ability to import nucleotides and short oligomers from their environment could potentially have replicated and retained larger genomic RNA oligonucleotides within a spatially defined compartment. We have previously shown that short 5′-phosphoroimidazolide-activated “helper” RNA oligomers enable the nonenzymatic copying of mixed-sequence templates in solution, using 5′-phosphoroimidazolide-activated mononucleotides. Here, we report that citrate-chelated Mg2+, a catalyst of nonenzymatic primer extension, enhances fatty acid membrane permeability to such short RNA oligomers up to the size of tetramers, without disrupting vesicle membranes. In addition, selective permeability of short, but not long, oligomers can be further enhanced by elevating the temperature. The ability to increase the permeability of fatty acid membranes to short oligonucleotides allows for the nonenzymatic copying of RNA templates containing all four nucleotides inside vesicles, bringing us one step closer to the goal of building a protocell capable of Darwinian evolution.

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在模型原细胞内复制混合序列 RNA 模板

RNA 在脂肪酸囊泡内的化学复制是细胞生命出现的一个合理的步骤。在原始地球上，能够从环境中输入核苷酸和短寡聚体的简单原始细胞可能会在空间限定的隔室内复制并保留更大的基因组 RNA 寡核苷酸。我们之前已经证明，使用 5'-磷酸咪唑活化的单核苷酸，短的 5'-磷酸咪唑活化的“辅助”RNA 寡聚体能够在溶液中非酶复制混合序列模板。在此，我们报道柠檬酸盐螯合的 Mg2+（一种非酶引物延伸的催化剂）可增强脂肪酸膜对此类短 RNA 寡聚物（高达四聚物大小）的渗透性，而不会破坏囊泡膜。此外，通过升高温度可以进一步增强短而非长低聚物的选择性渗透性。增加脂肪酸膜对短寡核苷酸的渗透性的能力允许在囊泡内非酶复制包含所有四种核苷酸的RNA模板，使我们离构建能够进行达尔文进化的原始细胞的目标又近了一步。