Polymers perform non-DNA evolution
19 April 2012
Scientists have found that six polymer alternatives to DNA can pass on genetic information, and have evolved one type to specifically bind target molecules.1 They say that their work reveals both broader chemical possibilities for these key life functions and provides a powerful tool for nanotechnology and medicine.
HNA could just as easily have been the molecule of life as DNA it now seems
Yet those processes don't normally work with the kind of unnatural nucleotides the team used. Consequently, MRC scientist Vitor Pinheiro first mutated and then selected polymerase enzymes that best processed 1,5-anhydrohexitol nucleic acid (HNA) and cyclohexenyl nucleic acid (CeNA) nucleotide trisphosphates. As well as isolating an enzyme that would make long enough polymers with all six XNA types to encode genetic information, he similarly engineered reverse transcriptases. Together the enzymes could accurately replicate genetic information from DNA to XNA and back, but with enough copying mistakes for functions to evolve. 'For the best ones it's 99% accurate or better,' Holliger tells Chemistry World. 'You really don't need more than that.'
Xeno-nucleic acids can store genetic information that can be processed into DNA and back again by mutated polymerases
Steven Benner, director of the Westheimer Institute at the Foundation for Applied Molecular Evolution in the US, notes that replacing DNA's sugar ring complements his team's introduction of non-standard nucleotide bases.2 'Together, these two classes of artificial chemical systems capable of heredity and evolution represents an expansion of our theories relating to the structure of molecules and the phenomenon of genetics,' he comments. 'It is relevant to biotechnology here on Earth as well as the possible forms that life might take throughout the cosmos.'
Jack Szostak, who investigates processes that allowed early chemical and biological evolution on the Earth at Harvard University, US, calls Holliger's team's work 'very exciting'. 'This is very interesting with respect to the origin of life,' he says. 'In principle, many different polymers could serve the roles of RNA and DNA in living organisms. Why then does modern biology use only RNA and DNA? The answer probably lies in two "filters". First, only some nucleic acids could actually be made on the early Earth. Second, of those polymers that actually could be made, some may have been functionally superior to others in terms of ease or accuracy of replication, or ability to generate catalytic folded structures.'
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1 V Pinheiro et al, Science, 2012, 336, 341 (DOI: 10.1126/science.1217622)
2 Z Yang et al, J. Am. Chem. Soc., 2011, 133, 15105 (DOI: 10.1021/ja204910n)
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