Scientists at The Scripps Research Institute (TSRI) report their synthesis of a form of the bacterium Escherichia coli with a genetic code that uses 21 basic amino acid building blocks to synthesize proteins --instead of the 20 found in nature.

This is the first time that anyone has created a completely autonomous organism that uses 21 amino acids and has the metabolic machinery to build those amino acids.

Life as we know it is composed, at the molecular level, of the same basic building blocks for instance, all life forms on Earth use the same four nucleotides to make DNA. And almost without exception, all known forms of life use the same common 20 amino acids --and only those 20-- to make proteins. The question is, why did life stop with 20 and why these 20?

A number of scientists have previously added unnatural amino acids to organisms, but most of these experiments involved eliminating the organism's supply of the natural amino acid and substituting a close relative. "So, in the end, you still have a 20 amino acid bacterium, but it's using an unnatural amino acid instead of the natural one," said Christopher Anderson, one author of the paper on this research led by Peter Schultz. "What our group really wanted to do is expand the genetic code, not just recode it. To do that, it takes a lot more effort. You have to come up with some way of specifically denoting how the protein is going to encode this 21st amino acid, because everything else in the genetic code already has a meaning associated with it." >from *Expanding the genetic code --TSRI scientists synthesize 21-amino-acid bacterium*, january 14, 2002

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> escherichia coli genetic expand