Life could have begun at the poles according to researchers in Germany.

Clemens Richert and Stephanie Vogel of the University of Karlsruhe have found that steps in the spontaneous replication of RNA are possible without the usual enzymes, even for the most difficult sections of the strand. 'The notion of spontaneous replication, perhaps the very reaction that defines the beginning of life from inanimate material, is fascinating,' said Richert. 'All attempts to demonstrate this phenomenon in vitro have thus far failed.'

Today, nucleic acid replication is catalysed by polymerases inside cells, but at some point in prebiotic evolution replication must have begun without these enzymes. 'It is likely that RNA was the first encoding system,' said Richert. But, the problem is that sequence stretches of multiple adenosine residues do not support spontaneous replication, he added.

RNA replication is assisted by three factors in Richert's system: promoters to aid nucleotide extension; helper RNA to assist in the replication of adenosine regions; and a low temperature, which helps to improve the yield of copied nucleotide. Even in the team's worst case situation, a stretch of three adenosine residues, the conditions allowed successful enzyme-free replication in a frozen mixture. 

According to Richert, the results suggest that the earliest life forms could have benefited from freezing environments. Chris Greenwell, an expert in prebiotic chemistry at the University of Wales in Bangor, UK, agrees. 'These experiments overcome the obstacle to replication presented by adenosine residues, lending support to theories that prebiotic replication occurred in polar ice-cap regions, where sea ice formation concentrates reactants,' he said.

However, Richert warned that 'the findings are only one step towards full spontaneous replication of RNA from mononucleotides. A system that causes the monomers to zipper up completely from one end of the original strand to the other, followed by dissociation of the new strand from the original is not yet within our reach.'

Michael Spencelayh