All living organisms and many “not quite alive” viruses use DNA as a repository of genetic information. Moreover, the principles on the basis of which DNA coding regions are used for the synthesis of other biomolecules, RNA and protein, are also universal.
It is the commonality of the genetic code that allows viruses to use cells to copy their own genomes and assemble new viral particles. It also makes possible the creation of GMOs and horizontal gene transfer – that is, borrowing the DNA of one cell from another, which is primarily characteristic of bacteria.
With all this chaotic flow of DNA, the authors of the new articles in a leading scientific journal Nature. They created a “genetic firewall” that stops foreign genes that carry viruses and so-called mobile genetic elements from entering the cell and outside (transposons). To do this, biologists have modified the genome of Escherichia coli (Escherichia coli) in such a way that the viruses in the end, in principle, were not able to infect it.
To begin with, the authors decided to simply remove some of the codons (the storage unit of genetic information in DNA, three consecutive nucleotides) from the bacterial genome. So they got a “compressed” genome (condensed) E. coliwhich uses only 61 codons instead of the usual 64. However, this did not work: some viruses were able to adapt to changes in the genome and still infect cells.
Therefore, the researchers switched to a different strategy: they changed the meaning of two codons – instead of one amino acid (serine), they began to code for another (leucine). The two molecules are very different, so replacing serine with leucine leads to a breakdown of the synthesized viral protein and the impossibility of copying the virus itself.
Indeed, the obtained strains of bacteria acquired resistance to all 12 viruses (bacteriophages) with which they were tried to infect.
It turned out that the “firewall” in DNA also effectively prevents the uncontrolled transfer of foreign genes, which was confirmed using a small circular DNA (plasmid). This is extremely important so that genes modified and transferred from one genome to another cannot get into the environment and some other organisms. This “gene leak” is one of the main concerns that limit the use of GMOs.
By the way, so that a new, virus-resistant and therefore more viable E. coli she herself could not “escape” from the laboratory and make trouble, scientists made her dependent on a special amino acid. In nature, this compound is absent, and therefore the modified bacterium simply will not survive there.
The new work is of great importance, because it can become the basis for obtaining cells that are completely insensitive to viruses and other forms of foreign genetic material. The authors hope that this opens up prospects for a radical solution to the problem of viral infections.