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Reprogrammed Bacterium Speaks New Language of Life
wabrandsma writes "New Scientist reports that 'A bacterium has had its genome recoded so that the standard language of life no longer applies. Instead, one of its words has been freed up to impart a different meaning, allowing the addition of genetic elements that don't exist in nature. ... The four letters of the genetic code are usually read by a cell's protein-production machinery, the ribosome, in sets of three letters called codons. Each codon "word" provides instructions about which amino acid to add next to a growing peptide chain. Although there are 64 ways of combining four letters, only 61 codons are used to encode the 20 amino acids found in nature. ... The three combinations left over, UAG, UAA and UGA, act like a full stop or period – telling the ribosome to terminate the process at that point. ... A team of synthetic biologists led by Farren Isaacs at Yale University have now fundamentally rewritten these rules (abstract). They took Escherichia coli cells and replaced all of their UAG stop codons with UAAs. They also deleted the instructions for making the release factor that usually binds to UAG, rendering UAG meaningless. Next they set about assigning UAG a new meaning, by designing molecules called tRNAs and accompanying enzymes that would attach an unnatural amino acid – fed to the cell – whenever they spotted this codon."
I would approve of requiring labeling on food if it was produced by one of these.
Sheesz people, we've been rprogramming trna to use nonnatural amino acides for over 10 years now! Theres even a few companies st up that do just that. The principle of trna modification is old, just their method is new
If an experiment works, something has gone wrong.
Codons are sets of three letters. Every creature has its own unique codon table - every three letters (GATC) make up one codon, so there are 64 possibilities. But the fun thing is that many codons actually code for the same amino acid, but take different times to complete the process. Either because some molecular rotation is taking place or just because it's a time delay to allow folding to complete elsewhere. Then sometimes the sequence is used in reverse order (creating a back-to-front version of whatever is made) and sometimes even the sequence of letters is read with an offset of one or two letters, so essentially one group of letters can code for six different chains of amino acids.
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Some years ago, when Venter's synthetic genome bacteria was created, I came up with a plan to do this on a more extensive scale.
(1) Sequence the genome of a bacterium, and edit the genome (on computer) to use no codons ending in 'T" or "A". (The redundancy of the genetic code allows this.)
(2) Also edit genome so that it has tRNA for the codons ending T or A which entirely change their meanings (but still using the standard amino acids.) (Transfer RNA - tRNA - are the mechanism by which the codon code is decyphered to amino acids.)
(3) Synthesize the edited genome, and replace the genome of a living bacterium with it. Breed for a few generations, to check that all is well, and to eliminate any of the old tRNA.
(4) Edit the genome to use entirely the new codons. Also edit replacement tRNA for the remaining codons, ending G or C.
(5) Replace the genome of one of our modified bacteria with this one.
Result: a bacterium which has an entirely rewritten genetic code, and is incapable of reading the old code.
However, I don't think I was the first to think this all up. In any case, Science didn't accept my letter proposing it.
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