E distribution over the 20 amino acids as well as the quit codon. Nevertheless, when assuming WT bias, differences may well happen, which depend on the specific randomized codon. The WT codon in our case is AGT, which can be one of many NNK codons but not among the list of NNS ones. Thus, under NNS randomization, the WT bias is avoided within this case, and also the required library size assuming