Unrau P J, Bartel D P
Whitehead Institute for Biomedical Research, and Department of Biology, MIT, Cambridge, Massachusetts 02142, USA.
Nature. 1998 Sep 17;395(6699):260-3. doi: 10.1038/26193.
The 'RNA world' hypothesis proposes that early life developed by making use of RNA molecules, rather than proteins, to catalyse the synthesis of important biological molecules. It is thought, however, that the nucleotides constituting RNA were scarce on early Earth. RNA-based life must therefore have acquired the ability to synthesize RNA nucleotides from simpler and more readily available precursors, such as sugars and bases. Plausible prebiotic synthesis routes have been proposed for sugars, sugar phosphates and the four RNA bases, but the coupling of these molecules into nucleotides, specifically pyrimidine nucleotides, poses a challenge to the RNA world hypothesis. Here we report the application of in vitro selection to isolate RNA molecules that catalyse the synthesis of a pyrimidine nucleotide at their 3' terminus. The finding that RNA can catalyse this type of reaction, which is modelled after pyrimidine synthesis in contemporary metabolism, supports the idea of an RNA world that included nucleotide synthesis and other metabolic pathways mediated by ribozymes.
“RNA世界”假说提出，早期生命是通过利用RNA分子而非蛋白质来催化重要生物分子的合成而发展起来的。然而，人们认为构成RNA的核苷酸在早期地球上很稀缺。因此，基于RNA的生命必定已经获得了从更简单、更易获取的前体（如糖和碱基）合成RNA核苷酸的能力。对于糖、糖磷酸酯和四种RNA碱基，已经提出了合理的前生物合成途径，但将这些分子偶联成核苷酸，特别是嘧啶核苷酸，对“RNA世界”假说构成了挑战。在此，我们报告了应用体外筛选来分离在其3'末端催化嘧啶核苷酸合成的RNA分子。RNA能够催化这类反应（该反应是以当代新陈代谢中的嘧啶合成作为模型）这一发现，支持了存在一个包括核苷酸合成和其他由核酶介导的代谢途径的RNA世界的观点。
