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 oligo nucleotides could have contributed to the origin of life and to the ev olution of a putative RNA world. In order to assess the fidelity of ol igonucleotide replication more accurately, chemical ligation reactions were performed with constant-sequence DNA templates and random-sequen ce DNA pools as substrates. Results: In keeping with earlier results, constant-sequence hairpin templates were not faithfully copied by rand om-sequence substrates. Linear templates, however, showed exceptional replication fidelity, particularly when random hexamers were ligated a t 25 degrees C. Surprisingly, at low temperatures the formation of G.A base pairs was common and sometimes occurred even more readily than t he formation of the corresponding Watson-Crick A-T and G-C base pairs. Conclusions: The fidelity of ligation reactions increases with temper ature 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 oligonucleotide s could readily have been generated by prebiotic mechanisms, it is pos sible that the earliest self-replicators arose via oligonucleotide lig ation.