The rate and fidelity of RNA self-replication based on nucleotide phosphoroimidazolides was further improved by the consideration of short helper oligonucleotides, which could bind downstream of the activated nucleotide monomers which take part in the primer extension reaction . The initial mechanistic rationale was that such a downstream oligonucleotide (or even mononucleotide) could bring closer phosphate group of incoming nucleotide to the 3 ′ end of a primer by conformational constraints inducing the formation of 3 ′ -5 ′ phosphodiester linkages . Furthermore, it was demonstrated that monomers and and helper oligonucleotides activated with 2-aminoimidazole yielded the highest rates of primer extension reaction (Fig. ) and b)). However, 2-aminoimidazole itself did not improve the rates and fidelities of nonenzymatic RNA self-replication of the A and U components.