Template switching between PNA and RNA oligonucleotides

THE origin of the RNA world1 is not easily understood, as effective prebiotic syntheses of the components of RNA, the β-ribofurano-side-5′-phosphates, are hard to envisage2. Recognition of this difficulty has led to the proposal1,3 that other genetic systems, the components of which are more easily formed, may have preceded RNA. This raises the question of how transitions between one genetic system and another could occur. Peptide nucleic acid (PNA) resembles RNA in its ability to form double-helical complexes stabilized by Watson-Crick hydrogen bonding between adenine and thymine and between cytosine and guanine4á¤-6, but has a backbone that is held together by amide rather than by phosphodiester bonds. Oligonucleotides based on RNA are known to act as templates that catalyse the non-enzymatic synthesis of their complements from activated mononucleotides7á¤-9, we now show that RNA oligonucleotides facilitate the synthesis of complementary PNA strands and vice versa. This suggests that a transition between different genetic systems can occur without loss of information.