"mutant" codon translations?

Question

AFAIK codon->protein translation is pretty much universal (very few exceptions). I've seen people explaining this means every living organism descends from the same ancestral. That's certainly a possibility, but perhaps any other translation would be extremely unlikely to evolve (chemically) and/or would end up evolving to the current one because it requires less energy (I'm speculating, but the tRNA could be simpler for example).

Are there evidences that it's possible to have a very different translation table? For example, an experiment in which the encoding of a couple of codons is swapped? I'm guessing this wouldn't work if genes are encoding more than one protein - but even if it did work, perhaps it would be too dangerous to have a lab leak of this mutant?

Answer 1

While the basis of the genetic code are highly conserved there are several variations that can actually be quite frequent. For example the mitochondria in your body use an encoding that is a little different from the cell nucleus.
As you stated, the most likely explanation for these small variations is evolution from an ancestral version.

Other encodings are clearly possible since all 64 possible triplets are used. Swapping the encoding can be achieved by modifying the enzymes that bring together t-RNAs and amino acids (so called t-RNA synthetases). This is quite complex and mainly done to enable the incorporation of new amino acids into proteins.

Not all potential codes would work equally well and might for example slow down translation. One possibility to completely alter the code without major problems would be to swap the first and second positions in each triplet.

And for your last question, an organism with a highly altered genetic encoding would actually be more save. This is because it would be impossible for this organism to exchange genetic information with its environment. Bacteria frequently obtain antibiotics resistances by gene transfer from other bacteria. The modified organism would not be able to make sense of a resistance gene obtained through this way.