Method for producing protein containing nonprotein amino acids - 1988, Miyazawa & Yokoyama et al. Description states: The present invention relates to a method for producing proteins comprising nonprotein amino acids (hereinafter referred to as non-natural proteins) using protein-producing organisms. The term "nonprotein amino acids" as used herein implicates all amino acids excluding the aforementioned 20 natural amino acids. Thus, all amino acids but the aforementioned 20 amino acids are referred to as nonprotein amino acids even if they are naturally present.
