Protein biosynthesis is a field that keeps coming up with new surprises. In the current issue of Nature researchers report that incorporation of a wrong amino-acid (carried by a wrong tRNA) increases the probability that the synthesis will be aborted after the next step, and also the probability that further errors are made which may then lead to termination.
This strikes me as a very expensive quality control system that indiscriminately weeds out significant errors and insignificant ones. Many amino acids can in fact be exchanged without endangering the folding or the function of the protein. Somebody should do a calculation of how economical this kind of error correction is, where the whole polypeptide chain synthesized so far is discarded because of one error that may or may not have an effect.
H. S. Zaher, R. Green, Nature 2008, 457, 161