Scientists have succeeded in reprogramming the genome of E. coli bacteria and obtaining the first living cells with an artificial genome that can create polymers from building blocks that do not occur in nature, following instructions embedded in their genes. These cells are also not susceptible to any viruses, Science reported referring to a new study.
In 2019, scientists created from scratch the largest synthetic genome in history – the genetically modified bacterium Escherichia coli (E. coli), reported Ria.ru.
The genetic code encoded in DNA consists of four bases, represented by letters: A, T, C, and G. Three-letter combinations called codons, when assembled, instruct the cell to add a certain amino acid to the chain, which it does with the help of molecules called tRNA (transport RNA). Each codon has a specific tRNA that recognizes it and adds the corresponding amino acid: for example, the tRNA that recognizes the TCG codon brings in the amino acid serine.
But four letters have 64 variants of three-letter combinations, and cells use only 20 natural amino acids in the construction. As a result, for each amino acid, there are several synonym codons that duplicate each other. For example, serine is encoded by TCG, TCA, AGC, and AGT codons. Even if one of them does not appear, the cell will continue to assemble in accordance with the genetic code.
Experimentally, scientists have made sure that cells can make normal proteins, live and grow, even if three codons out of four are removed. Then the authors completely ‘rewrote’ the E. coli genome, significantly simplifying it and removing all synonymous codons. This made E. coli cells completely immune to viruses, since viruses use the complete genetic code, and modified bacteria do not have a tool to read specific viral genes.
Scientists later applied this same technology to create the first cell that can collect polymers entirely from building blocks that do not occur in nature.
The ability to generate designer proteins and plastics using unnatural building blocks will open up countless applications, from developing new classes of biotherapeutic agents to biomaterials with innovative properties.