Sorbonne Université, Museum National d'Histoire Naturelle, CNRS MNHN UMR 7205, Institut de Systématique, Evolution, Biodiversité, ISYEB, F-75005 Paris, France.
Institute for Integrative Biology of the Cell (I2BC), CNRS, CEA, Université Paris Sud, F-91198 Gif-sur-Yvette, France.
Viruses. 2019 Mar 21;11(3):283. doi: 10.3390/v11030283.
Current cellular facts allow us to follow the link from chemical to biochemical metabolites, from the ancient to the modern world. In this context, the "RNA world" hypothesis proposes that early in the evolution of life, the ribozyme was responsible for the storage and transfer of genetic information and for the catalysis of biochemical reactions. Accordingly, the hammerhead ribozyme (HHR) and the hairpin ribozyme belong to a family of endonucleolytic RNAs performing self-cleavage that might occur during replication. Furthermore, regarding the widespread occurrence of HHRs in several genomes of modern organisms (from mammals to small parasites and elsewhere), these small ribozymes have been regarded as living fossils of a primitive RNA world. They fold into 3D structures that generally require long-range intramolecular interactions to adopt the catalytically active conformation under specific physicochemical conditions. By studying viroids as plausible remains of ancient RNA, we recently demonstrated that they replicate in non-specific hosts, emphasizing their adaptability to different environments, which enhanced their survival probability over the ages. All these results exemplify ubiquitous features of life. Those are the structural and functional versatility of small RNAs, ribozymes, and viroids, as well as their diversity and adaptability to various extreme conditions. All these traits must have originated in early life to generate novel RNA populations.
目前的细胞事实使我们能够追踪从化学到生化代谢物的联系，从古代到现代世界。在这种背景下，“RNA 世界”假说提出，在生命进化的早期，核酶负责遗传信息的存储和传递，并催化生化反应。因此，锤头核酶（HHR）和发夹核酶属于一类具有自我切割活性的内切核酸酶 RNA，这种自我切割可能发生在复制过程中。此外，鉴于 HHR 在现代生物体（从哺乳动物到小型寄生虫等）的几个基因组中的广泛存在，这些小核酶被认为是原始 RNA 世界的活化石。它们折叠成 3D 结构，通常需要长程分子内相互作用才能在特定物理化学条件下采用催化活性构象。通过研究类病毒作为古代 RNA 的可能残留物，我们最近证明它们在非特异性宿主中复制，这强调了它们对不同环境的适应性，从而提高了它们在不同时期的生存概率。所有这些结果都体现了生命的普遍特征。这些特征包括小 RNA、核酶和类病毒的结构和功能多样性以及它们对各种极端条件的适应性。所有这些特征都必须起源于早期生命，才能产生新的 RNA 群体。
