Patent ID: 8183013

Claim:
A method for producing a target protein into which a non-natural amino acid has been incorporated, wherein said method comprising the steps: (a) transforming a prokaryotic host cell with a mutant gene encoding an E. coli -derived mutant tyrosyl tRS and an E. coli -derived suppressor tyrosine tRNA capable of binding to the non-natural amino acids, wherein said mutant tyrosyl tRS has a higher specificity for the non-natural amino acid compared to specificity for tyrosine and wherein said E. coli host cell further expresses a eukaryote-type tyrosyl-tRNA synthetase and tRNA genes specific for tyrosine; and (b) knocking out the endogenous tyrosyl-tRNA synthetase and tyrosine tRNA genes of the E. coli host cell; and (c) culturing the host cell in a medium thereby expressing the target protein into which a non-natural amino acid is incorporated at the site encoded by the codon to be suppressed.