Real genetic engineering – the recoding of E.coli

e coliby NIAID

Researchers advance toward engineering ‘wildly new genome’
[Via Eureka! Science News – Popular science news]

In two parallel projects, researchers have created new genomes inside the bacterium E. coli in ways that test the limits of genetic reprogramming and open new possibilities for increasing flexibility, productivity and safety in biotechnology.


What these guys did is pretty amazing. They created a way to put entirely new metabolic pathways and proteins into bacteria.

Three nucleic acids in a row are called a codon if used for the translation of mRNA into protein. Every gene terminates in a specific codon that ‘stops’ translation, which is then recognized by specific machinery to turn off the translation machinery.

As it turns out, there are 3 stop codon – UAG, UAA, and UGA.  But only 326 of the UAG codons are found in the entire E. coli genome. So, they first altered ever UAG codon to UAA. 

This would have no difference on gene expression as there are still stop codons where they are needed.

They also deleted the translation machinery that worked with UAG so that there was no way any UAG that was found would act as a stop codon. So they now had bacteria that worked fine but had a complete lack of a single codon – UAG.

This allowed them to insert a whole set of new translation machinery that actually added a specific amino acid to the translated protein when it found a UAG codon. INstead of a stop codon, UAG acted like any other codon for adding amino acids to protein,  a sense codon.

They were able to show that a gene containing UAG in this modified bacteria would not be made unless the correct translation machinery was present. And if it was, the modified gene was expressed fine in the modified bacteria.

So, this now allows us to add certain specific unusual amino acids at specific places in any protein we might want to  examine.

And that is pure genetic engineering.