Patent ID: 7736899

Claim:
A method for providing bacterial or yeast cells with the capacity to produce a protein, the amino acid sequence of which comprises at least one unconventional amino acid, comprising: (a) introducing at least one missense mutation in a target codon of a gene encoding a protein required for the growth of the bacterial or yeast cells, wherein the mutated protein synthesized from the mutated gene is not functional in the bacterial or yeast cells; and (b) selecting the bacterial or yeast cells obtained in (a) in a culture medium which (1) does not contain a nutrient compensating for the loss of functionality of the mutated protein and (2) contains an unconventional amino acid which restores the functionality of said protein required for growth of the bacterial or yeast cells, said unconventional amino acid being that encoded by said target codon; and (c) culturing the bacterial or yeast cells obtained in (b) in a culture medium containing said amino acid encoded by said target codon.