The two new letters of the genetic alphabet

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A team from the Scripps institution in California, announced that it managed to insert two nucleotides into a bacterium “E. coli” (in the photo).

Any form of life on Earth is based on four “letters” (A, C, T, G) which, laid end-to-end, form genes, as those of bacteria than ours. Scientists are now beginning to add two letters to the alphabet — and that a bacterium is able to use it.


Already in 2014, a team from the Scripps institution in California, announced in the journal Nature, has managed to insert two additional letters — or nucleotides — dubbed X and Y, in the bacterium E. coli. Nucleotides that had then been passed on to following generations, each time that the bacteria are divided. It remained to be seen if these additional letters were functional, and that is what a team from the Scripps institution, always led by Floyd Romesberg, department of chemistry, claims to have accomplished : to produce new proteins on demand, we read in the edition of 29 November of that Nature.


In the long term, the objective is to produce proteins that have pharmaceutical use, but which are, for the moment, not naturally produced by living beings. The researchers have demonstrated that it was possible for a bacterium to produce such proteins as ” foreign “, and that it was possible to retrieve them. Remains to be seen if they will produce proteins that will be used to something, rather than being simply a scientific curiosity.

Genetic Alphabet

A, C, T, G : a human has 3 billion of these letters ” without spaces or punctuation “.


Pairs of bases : because these four letters always come in pairs, called base pairs. The idea to create pairs of bases, “foreign” dates back to the 1960s, and the team from the Scripps institution and has since the late 1990s.


Gene : each gene is composed of a variable number of base pairs.


Protein : the genes that are of interest here, the geneticists are those that are able to produce proteins essential for the proper functioning of a living being. The idea behind this research in “synthetic biology” is to create bacteria from which a gene would be able to produce proteins in response to a need specific medical.