Semi-artificial living creature: Scientists have created the first bacteria that translates a pair of artificial DNA letters

The two pairs known in nature - AT and CG are joined by a new pair d5SICS-dNaM in an E. coli bacterium that succeeded in replicating them well. In this way, it will be possible to create completely new biological products ranging from medicines to nanotechnology

Scientists at the Script Research Institute in California have succeeded in engineering a bacterium whose genetic material contains an extra pair of DNA letters - a base that does not exist in nature. The bacterial cell can replicate the artificial DNA base more or less normally, as long as it is provided with the molecular building blocks.

Life on Earth, despite all its diversity, is coded using two pairs of DNA bases: the pair AT and CG and now we have created an unnatural third pair" said Prof. Floyd Rumsberg from TSRI University who led the research.

"This shows that other solutions for storing genetic information are possible and, of course, this will allow us to advance to expanded DNA biology that can provide many applications - from medicines to new types of nanotechnology.

The achievement was reported May 7 in an early online publication of the journal Nature.

Romesberg and his colleagues have been searching since the late nineties for pairs of molecules that could be used as new DNA bases - and in particular, those that could code for proteins and even living things that never existed.

The task was not easy. Each pair of DNA bases will be required to pair in a compatible manner with the natural bases adenine-thymine and cytosine-guanine. These new bases will be required to line up alongside the natural bases in DNA Research's DNA. They will be required to separate and come back together smoothly when polymerase enzymes are activated on them during the rewriting of the DNA and its transcription into RNA. In some way, these replicators will have to evade attack and elimination by the DNA's natural repair mechanisms.

Despite these challenges, in 2008 Rumsberg and his colleagues announced that they had made an important step towards the goal. In a study published at the time, they identified a series of nuclear molecules that can connect to the double helix of DNA almost like the natural base pairs and showed that DNA containing these unnatural base pairs can replicate in the presence of the right enzymes. In another study in the same year, the researchers showed that they were able to find enzymes that reproduce the semi-synthetic DNA into RNA.

However, the work was too simplistic and it was done in a test tube. "These unnatural base pairs worked well in vitro but the challenge was to make them work in the more complex environment of the living cell" said Denis Malishev, Romesberg's lab member, who was the lead researcher on the new study.

Microalgae led to the breakthrough

In the new study, the team synthesized a strand of circular DNA known as a plasmid and inserted it into a cell of the famous bacterium E. coli. The DNA of the plasmid contained natural TA and CG pairs together with the best base pairs that were able to be produced in the laboratory, the molecules are known as: d5SICS and dNaM. The goal was to convince the E cells. coli to replicate the semi-synthetic DNA as normally as possible.

The biggest barrier may have been the promise to those who fear the uncontrolled release of a new life form - the two building blocks do not exist naturally, so to convince the E. coli to replicate the DNA containing them, the researchers provided the molecular building blocks (called triphosphates) artificially by adding them to the liquid solution outside the cell. Then, to get them into the cells they needed special triphosphate transfer molecules to do the job.

The researchers were able to find such a transporter, a molecule found in a species of microalgae, that was good enough to make this insertion. "This was our big breakthrough - which made it possible to build the bacterium with the additional bases.

More of the topic in Hayadan:

A transgenic bacterium with synthetic DNA

Only 12% of the genetic material in bacteria is essential for life

Although the completion of the project took another year, no more obstacles were discovered. The team members discovered to some degree of surprise that the semi-synthetic plasmid replicated with reasonable speed and accuracy, did not interfere with the growth of the bacterial cells and showed no signs of loss of the unnatural base pairs by the DNA repair mechanisms.

Now we have stopped the flow of the artificial building blocks (triphosphate), the turnover rate of the d5SICS-dNaM together with the natural base pairs were well suited to the cell's own replication mechanism - and it does not appear that any factor 'expelled' the new pair" said Malishev. "It is important to note that the two breakthroughs also provide control over the system. Our new bases can only enter the cell if we turn on the protein transport protein. Without this protein or when the new bases are not supplied, the cell will revert to A,T,C,G while d5SICS and dNaM will disappear from the genome.

The next step will be to demonstrate that the transcription inside the cell of the thousand byte letters of the DND into RNA that can feed a mechanism that creates proteins in the cell. "Basically, we can encode proteins made of new and artificial amino acids - something that will give us more power than ever to tailor proteins for healing and diagnostic purposes, as well as use them in the laboratory to obtain new properties," said Romesberg. "Additional applications such as nano materials are also possible."

The research was partially funded by the US National Institutes of Health.

For information on the Scripts Research Institute website