"can," "may," ... 1) My argument was simply that the limit on recodable codons is much higher than two, as it was claimed in the article. That's hard to argue

"can," "may," ... 1) My argument was simply that the limit on recodable codons is much higher than two, as it was claimed in the article. That's hard to argue with. I didn't say the result in every case would be neutral mutations. 2) The consequences of recoding the stop codons are also not neutral. For example, when Isaacs (eventually) did it, there were severe growth phenotypes in the resulting strain. So I agree that "it's not that simple," which is frankly why I'm not hugely optimistic about this class of endeavors. But the point stands that there is no need in principle for a 4-base code.