2014-03-02 12:42:52
One of the reasons for the universality of life is that it mostly shares the same genetic code, that is, the information contained in DNA is written in the same language for all organisms. This language translates the letter sequence of DNA into amino acid sequences of proteins. For example, the letters ATG stand for the amino acid methionine; the letters CCC, the amino acid proline; and the letters UAG, “stop”, meaning that the synthesis of the protein must be stopped.
The universality of the genetic code can be explained by several reasons. One of the most important is that probably, after the origin of life, not all genetic languages were equally effective and efficient in ensuring survival, and the universal language that we have today was probably the most suitable for the primitive organisms that used it. they developed. An additional advantage is that the same genetic language allows genes to be transferred between different organisms. Thus, bacteria transmit antibiotic resistance genes to each other, which helps them survive. However, a universal genetic code also generates drawbacks. For example, the same genetic code allows viruses to cross the species barrier and be more virulent. It is believed that the AIDS virus appeared precisely through this mechanism.
PROBLEMS AND SOLUTIONS
The universal genetic code raises a series of problems, not only scientific but, above all, technological. One of the most serious is that genetically modified organisms can escape into the environment and transfer the genes they have introduced to other organisms in their ecosystem. Furthermore, the attack of viruses on bacteria is also a serious problem that limits the use of these microorganisms to manufacture proteins of health or technological interest. Finally, an additional drawback is that the genetic code is limited to the use of 20 amino acids, which, although it may be the optimal situation for life, is not necessarily optimal for its technological use.
For the above reasons, modifying the genetic code in a bacteria, that is, modifying the universal language of genes, could solve some of these problems. Firstly, this genetically recoded organism – which had had the meaning of at least one triplet of letters, a “word”, in the DNA modified – would be genetically isolated from the rest of Nature. The genes that it could receive from other bacteria, or the genes from viruses that could infect it, would not be translated correctly, as they are different genetic languages. For this same reason, they could not modify other bacteria or organisms by accidental transfer of their genes and would also be resistant to viruses. Additionally, these organisms could produce new proteins by containing at least one additional amino acid not present in natural proteins.
A LITTLE BIG CHANGE
Changing the genetic code of an organism and leaving it alive is not an easy task. However, researchers from several American universities and research centers have achieved it, publishing these results in the journal Science. To achieve this, the researchers used the property of redundancy of the genetic code, that is, the property of using several “words” with the same meaning. This redundancy is also typical of human languages, since many words have synonyms. In the case of the genetic code, for example, the three words UAG, UAA, and UGA mean “stop.” This redundancy makes it possible to replace one of these words in the genome with another equivalent one without affecting the code to produce proteins correctly.
The researchers chose to replace the word UAG with its synonym UAA throughout the genome of the Escherichia coli bacteria. The word UAG was selected because it was known that these three letters are the least frequent in the genome of the bacteria (it only contains 321 UAGs), which made their replacement easier. Furthermore, previous studies had proven that it was possible to use this triplet of letters to incorporate new amino acids into proteins, since the components of the translation machinery to achieve this had been produced by other laboratories.
Thus, if we replace all the UAG triplets with UAA in the genome of the bacteria, the new code will continue to stop protein synthesis correctly, but we will have freed the word UAG from its meaning and now we will be able to give it a new one of interest: a new amino acid. To do this, the researchers eliminated the factor that interprets the word UAG as “stop.” This factor, called RF1, is produced by a gene that can be deleted from the bacteria’s genome. After eliminating this factor, the researchers introduced new genes to the bacteria that allowed it to interpret the word UAG as a new amino acid. In this way, scientists have been able to generate a new bacteria to which they can incorporate genes with UAG words that, instead of stopping protein synthesis, incorporate an unnatural amino acid into them.
We lack space here to explain in more detail the techniques used by scientists to generate the first recoded organism in history, but the fact is that this microorganism exists and promises to be the first in a series of genetically recoded organisms that can be used to the production of drugs, or biological products of health interest, in a safer way than what has been done until now.
NEW WORK BY JORGE LABORDA.
It can be purchased here:
Chained circumstances. Ed. Lulu
Other works by Jorge Laborda
One Moon, one civilization. Why the Moon tells us that we are alone in the Universe
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