Non-enzymatic assembly of active chimeric ribozymes from aminoacylated RNA oligonucleotides

Abstract

Aminoacylated tRNAs, which harbor a covalent linkage between amino acids and RNA, are a universally conserved feature of life. Because they are essential substrates for ribosomal translation, aminoacylated oligonucleotides must have been present in the RNA World prior to the evolution of the ribosome. One possibility we are exploring is that the aminoacyl ester linkage served another function before being recruited for ribosomal protein synthesis. The nonenzymatic assembly of ribozymes from short RNA oligomers under realistic conditions remains a key challenge in demonstrating a plausible pathway from prebiotic chemistry to the RNA World. Here, we show that aminoacylated RNAs can undergo template-directed assembly into chimeric amino acid-RNA polymers that are active ribozymes. We demonstrate that such chimeric polymers can retain the enzymatic function of their all-RNA counterparts by generating chimeric hammerhead, RNA ligase, and aminoacyl transferase ribozymes. Amino acids with diverse side chains form linkages that are well tolerated within the RNA backbone, potentially bringing novel functionalities to ribozyme catalysis. Our work suggests that aminoacylation chemistry may have played a role in primordial ribozyme assembly. Increasing the efficiency of this process provides an evolutionary rationale for the emergence of sequence and amino acid specific aminoacyl-RNA synthetase ribozymes, which could then have generated the substrates for ribosomal protein synthesis. Significance StatementThe emergence of the primordial ribosome from the RNA World would have required access to aminoacylated RNA substrates. The spontaneous generation of such substrates without enzymes is inefficient, and it remains unclear how they could be selected for in a prebiotic milieu. In our study we identify a role for aminoacylated RNA in ribozyme assembly, a longstanding problem in the origin of life research. We show that aminoacylated RNAs, but not unmodified RNAs, rapidly assemble into chimeric amino acid-bridged ribozymes that retain their native enzymatic activity. Our work therefore addresses two key challenges within the origin-of-life field: we demonstrate assembly of functional ribozymes and we identify a potential evolutionary benefit for RNA aminoacylation that is independent of coded peptide translation.