Molecular alternatives to life offer new insight into evolution

Washington -  Researchers have successfully replicated the chemistry of life in synthetic versions of DNA and RNA molecules, thus indicating that the pair of nucleic acids are not unique in  their capability to encode information and to pass it on through heredity.

Living systems owe their existence to a pair of information-carrying molecules: DNA and RNA.

These fundamental chemical forms possess two features essential for life: they display heredity—meaning they can encode and pass on genetic information, and they can adapt over time, through processes of Darwinian evolution.

A long-debated question is whether heredity and evolution could be performed by molecules other than DNA and RNA.

John Chaput, a researcher at ASU's Biodesign Institute joined a multidisciplinary team of scientists from England, Belgium and Denmark to extend these properties to other so-called  Xenonucleic acids or XNA's.

The group demonstrated for the first time that six of these unnatural nucleic acid polymers are capable of sharing information with DNA.

One of these XNAs, a molecule referred to as anhydrohexitol nucleic acid or HNA was capable of undergoing directed evolution and folding into biologically useful forms.

The work sheds new light on questions concerning the origins of life and provides a range of practical applications for molecular medicine that were not previously available.

Nucleic acid aptamers, which have been engineered through in vitro selection to bind with various molecules, act in a manner similar to antibodies—latching onto their targets with high  affinity and specificity.

“This could be great for building new types of diagnostics and new types of biosensors,” Chaput said, pointing out that XNAs are heartier molecules, not recognized by the natural enzymes  that tend to degrade DNA and RNA.

New therapeutics may also arise from experimental Xenobiology.

The process of evolution was encouraged in the lab; one of their DNA analogues was designed to cling to a particular protein or RNA target, those that failed to do so were washed away.

As successive copies of those that stuck were made, variations in the genetic code - and the consequent structure the molecules took on - led to ever more tightly attached XNAs.

“We've been able to show that both heredity - information storage and propagation - and evolution, which are really two hallmarks of life, can be reproduced and implemented in alternative  polymers other than DNA and RNA,” Dr Philipp Holliger of the UK Medical Research Council's Laboratory of Molecular Biology explained.

“There is nothing 'Goldilocks' about DNA and RNA - there is no overwhelming functional imperative for genetic systems or biology to be based on these two nucleic acids,” Dr Holliger

added.

The study has been published in the current issue of Science.