Perfect PNA pairing

Peptide nucleic acids that can respond dynamically to selection pressures bolster the case for the interdependence of peptides and nucleic acids in early genetic systems

Credit: © 2009 AAAS

Nucleic acids are well established as the basis of genetic information storage, but their relatively complex structure can be difficult to reconcile with the spontaneous origin of genetic systems. Several nucleic acid analogues have been reported, but so far none have shown the ability to respond to selection pressures in the absence of enzymes.

Now, Reza Ghadiri and colleagues have prepared¹ a peptide nucleic acid (PNA) in which nucleobases are anchored — by a thioester linkage — to a peptide backbone in which every alternate amino acid is cysteine. The team, from the Scripps Research Institute and the Salk Institute for Biological Studies in California, show that the sequence of nucleobases in the PNA can be rapidly exchanged from a library containing an excess of different nucleobases. Furthermore, they show that the exchange can be directed by the presence of a fixed template strand of nucleic acid — the template strand will specifically remove complementary strands of PNA (those with the right sequence) from the equilibrium. The remaining unbound PNAs and free nucleobases equilibrate to form more of the 'correct' complementary sequence.

Such adaptability is a characteristic feature of living systems and could be advantageous for the design of biomaterials that are capable of self-repair.