Changing genetic code of E. coli to accept synthetic amino acids? I read in my Biology textbook that an experiment has been done in which one of E. coli's stop codon has been altered to accept a synthetic amino acid. I do not get how it can be done. Taking the fact into account that every permutation of the 4 natural nitrogenous bases codes for a particular amino acid means that if the stop codon, let's say UGA, is altered to UUA it will code for Leucine. How does this leave a possibility for the production of a codon which codes for a synthetic amino acid? I will appreciate your kind explanation. Thank you a lot.

This has been done by engineering a synthetic tRNA that can recognize the stop codon. The synthetic tRNA possesses a non-natural amino acid that is processed normally by the Ribosome and incorporated into the growing polypeptide chain.