As you know, in order to encode a huge amount of information in the genetic code, only 4 nucleic acids are used: adenine, guanine, thymine and cytosine. In the genetic code, they are denoted by corresponding letters – A, G, T and C. Thus, we can say that the "genetic alphabet" consists of 4 letters, and until recently it was thought that it can not be changed, but the group of scientists from the Scripps Institute for the first time managed to complete it with two new letters and at the same time leave it fully functioning.
In all living organisms, the above-described nucleic acids are joined together not by any means but by the principle of complementarity. That is, they seem to "look" at each other, and opposite A should always be T, and opposite G – C, and nothing else. But it's still half the battle. These letters should "add up to words", which are called triplets – special combinations, thanks to which all the main points like reading information, encoding proteins, and so on occur. A few years ago, Science magazine published an article describing the experience in which transport RNAs brought to DNA a new amino acid that was recognized and embedded in the code. However, this acid was only one, did not have a pair and did not perform a new function.
In a new study, researchers from Synthorx used two new nitrogenous bases (designated X and Y). They are opposite each other in the double-stranded DNA molecule, just like the standard 4 bases, but unlike them, "new letters" are connected not by hydrogen bonds, but by hydrophobic ones. Moreover, having built two new bases in bacterial DNA, the latter were able to reproduce them, but these bacteria initially divided more slowly than usual and sometimes replaced the new DNA with "traditional" DNA. Now bacteria have been eliminated, which reproduce new DNA without problems. It remains only to come up with these letters for new triplets.
"If you count how many triple combinations you can get with four letters on your hands, we get 64 combinations, adding only two letters, we expand the number of possible genetic words to 216, and as a result, it will be possible to encode more 172 amino acids, which opens up a vast space for bioengineering. "