Assembly of a functional ribozyme from short oligomers by enhanced non-enzymatic ligation

The non-enzymatic replication of the primordial genetic material is thought to have enabled the evolution of the first ribozymes, leading to early forms of RNA-based life. However, the reported rate of chemical RNA ligation is extremely slow. Here we show that the rate of ligation can be greatly enhanced by employing a 3ʹ-amino group at the 3ʹ-end of each oligonucleotide, in combination with an N-alkyl imidazole organocatalyst. These modifications allow the rapid copying of long RNA templates by multi-step ligation of tetranucleotides, as well as the assembly of long oligonucleotides from short template splints. Our work shows that a functional RNA ligase ribozyme can be assembled from relatively short oligonucleotides, demonstrating a transition from non-enzymatic ligation to enzymatic ligation. We suggest that the genomes of primitive protocells could have consisted of relatively easily replicated oligonucleotides as short as 10 to 12 nucleotides in length.