A method for improving the quality and homogeneity of recombinant expression of a peptide of interest encoded by a first nucleotide sequence , said method comprises the steps of: - putting into contact a host cell with a cassette sequence or a vector comprising said cassette, the cassette comprising: - a first nucleotide sequence encoding said peptide of interest to be produced by said host cell , said nucleotide sequence being upstream of and linked to - a second nucleotide sequence either providing a resistance to a toxin that is toxic for said host cell or encoding an antitoxin peptide to a toxin , wherein said first nucleotide sequence and second nucleotide sequence are linked to encode their corresponding peptides as a fusion protein and - between the first nucleotide sequence and the second nucleotide sequence , a third nucleotide sequence encoding a linker peptide producing two peptides after cleavage and having a length comprised between 2 and 500 amino acids and wherein said first, second and third nucleotide sequences are organized in such a way that production of the antitoxin peptide encoded by the second nucleotide sequence(s) is translationally coupled to production of the peptide of interest encoded by the first nucleotide sequence as a fusion protein , with either the host cell comprising in its genome, preferably under the control of a promoter/operator sequence , one or more copies of a fourth nucleotide sequence encoding a toxin which is toxic for said host cell and/or with said host cell being present in a culture medium comprising said toxin and/or comprising a cell different from the host cell secreting in said culture medium, said toxin , and - recovering from said host cell medium, either the fusion protein or the peptide of interest , possibly after a cleavage of the linker peptide . - putting into contact a host cell with a cassette sequence or a vector comprising said cassette, the cassette comprising: - a first nucleotide sequence encoding said peptide of interest to be produced by said host cell , said nucleotide sequence being upstream of and linked to - a second nucleotide sequence either providing a resistance to a toxin that is toxic for said host cell or encoding an antitoxin peptide to a toxin , wherein said first nucleotide sequence and second nucleotide sequence are linked to encode their corresponding peptides as a fusion protein and - between the first nucleotide sequence and the second nucleotide sequence , a third nucleotide sequence encoding a linker peptide producing two peptides after cleavage and having a length comprised between 2 and 500 amino acids and wherein said first, second and third nucleotide sequences are organized in such a way that production of the antitoxin peptide encoded by the second nucleotide sequence(s) is translationally coupled to production of the peptide of interest encoded by the first nucleotide sequence as a fusion protein , with either the host cell comprising in its genome, preferably under the control of a promoter/operator sequence , one or more copies of a fourth nucleotide sequence encoding a toxin which is toxic for said host cell and/or with said host cell being present in a culture medium comprising said toxin and/or comprising a cell different from the host cell secreting in said culture medium, said toxin , and - recovering from said host cell medium, either the fusion protein or the peptide of interest , possibly after a cleavage of the linker peptide . <EOS>