Simplification of the genetic code

During the past decade the most popular exercise that biochemists performed with the genetic code was its expansion via incorporation of unnatural amino acids. Only last year they tried to reverse the task and to simplify, rather than complexify, the genetic code by excluding certain amino acids from it. A few days ago an article appeared in ACS Synthetic Biology which describes the code where four amino acids (Asn, Cys, Trp and Tyr) were excluded and their codons were reallocated to amino acid serine (Ser), which thus has 13 codons in this code:

While expansion of the genetic code with unnatural amino acids is normally performed within living cells, the simplification of the code like that shown above is achieved, certainly, in a cell-free extract. Living cells will not survive radical modification of all its proteins (however, another recent experiment has shown that E. coli might live in fact with one of the amino acids – tryptophan – eliminated from the proteome).