Surprising fidelity of template-directed chemical ligation of oligonucleotides

Background: Nucleic acid replication via oligonucleotide ligation has been shown to be extremely prone to errors, If this is the case, it is difficult to envision how the assembly and replication of short oligonucleotides could have contributed to the origin of life and to the evolution of a putative RNA world. In order to assess the fidelity of oligonucleotide replication more accurately, chemical ligation reactions were performed with constant-sequence DNA templates and random-sequence DNA pools as substrates. Results: In keeping with earlier results, constant-sequence hairpin templates were not faithfully copied by random-sequence substrates. Linear templates, however, showed exceptional replication fidelity, particularly when random hexamers were ligated at 25 degrees C. Surprisingly, at low temperatures the formation of G.A base pairs was common and sometimes occurred even more readily than the formation of the corresponding Watson-Crick A-T and G-C base pairs. Conclusions: The fidelity of ligation reactions increases with temperature and decreases with the length of the random-sequence substrates. Oligonucleotides with a defined sequence can be copied faithfully in the absence of enzymes. Thus, to the extent that short oligonucleotides could readily have been generated by prebiotic mechanisms, it is possible that the earliest self-replicators arose via oligonucleotide ligation.