Genetic code 2.0: Life gets a new operating system

18:00 14 February 2010 by Linda Geddes

A new way of using the genetic code has been created, allowing proteins to be made with properties that have never been seen in the natural world. The breakthrough could eventually lead to the creation of new or "improved" life forms incorporating these new materials into their tissue.

In all existing life forms, the four "letters" of the genetic code, called nucleotides, are read in triplets, so that every three nucleotides encode a single amino acid.

Not any more. Jason Chin at the University of Cambridge and his colleagues have now redesigned the cell's machinery so that it reads the genetic code in quadruplets.

In the genetic code that life has used up to now, there are 64 possible triplet combinations of the four nucleotide letters; these genetic "words" are called codons. Each codon either codes for an amino acid or tells the cell to stop making a protein chain. Now Chin's team have created 256 blank four-letter codons that can be assigned to amino acids that don't even exist yet.

Fundamental redesign

To achieve this, the team had to redesign three pieces of the cellular machinery that make proteins.

But they didn't stop there. The team went on to prove their new genetic code works by assigning two "unnatural" amino acids to their quadruplet codons, and incorporated them into a protein chain.

"It's the beginning of a parallel genetic code," says Chin.

Stronger bonds

What's more, they've shown that these amino acids can react with each other to form a different kind of chemical bond to those which usually hold proteins together in their three-dimensional shape.

The normal kind of bonds – disulphide bonds – can be broken by changes in heat and acidity, causing proteins to lose their 3D structure. This, for instance, is why egg whites change colour and texture when cooked: as the albumen in the whites loses its structure, its physical appearance is transformed.

But the bonds created between Chin's new amino acids are stronger – and so could allow proteins to work in a much wider range of environments. This could help make drugs that can be taken orally without being destroyed by the acids in the digestive tract, for instance.

But that's just the beginning. In the longer term it might be possible to create cells that produce entirely new polymers, such as plastic-like materials. Organisms made of these cells could incorporate the stronger polymers and become stronger or more adaptable as a result.

"It's a very impressive advance that opens up new theoretical horizons in synthetic biology," says genomics pioneer Craig Venter, who heads his own institute in Rockville, Maryland, and is currently trying to create a synthetic organism from scratch.

From: http://www.newscientist.com/article/dn18523-dna-20-a-new-operating-system-for-life-is-created.html