that DNA is the only molecule that can encode genetic material? Think
Philipp Holliger of the MRC Laboratory of Molecular Biology and his team
has created a man-made genetic material called the XNA (as science fiction
fans worldwide all ponder, what could possibly go wrong?):
Holliger’s team focused on six XNAs (xeno-nucleic acids). DNA and
RNA are made of a sugar, a phosphate and a base. The XNAs had different
sugars, and in some of them the sugars are replaced with completely
A key hurdle for the team was to create enzymes that could copy
a gene from a DNA molecule to an XNA molecule, and other enzymes that
could copy it back into DNA.
They started with enzymes that do this in DNA only. Over the years
the team made incremental tweaks until they produced enzymes that could
work on XNAs.
Once they had created these enzymes, they were able to store information
in each of the XNAs, copy it to DNA, and copy it back into a new XNA.
In effect, the first XNA passed its information on to the new one –
albeit in a roundabout way. “The cycle we have is a bit like a
retrovirus, which cycles between RNA and DNA,” Holliger says.
This is the first time artificial molecules have been made to pass
genes on to their descendants. Because the XNAs can do this, they are
capable of evolution.
“The immediate question is whether these XNAs can be introduced
into cells,” says Farren Isaacs of Yale University in New Haven,
Connecticut. Once the XNAs were installed, they could replicate and
evolve on their own. “That would be remarkable.”