Patent ID: 7183097

Claim:
A method of confining an extrachromosomal replicon to a recombinant microbial cell population, said method comprising: (i) isolating a microbial cell which naturally comprises in the chromosome a gene coding for a cytotoxin polypeptide of a proteic killer gene system or introducing said gene coding for a cytotoxin polypeptide of a proteic killer gene system into the chromosome of a cell which does not naturally comprise said gene; (ii) introducing into said cell an extrachromosomal replicon to be confined, wherein said replicon comprises a gene coding for a gene product of interest and a gene coding for an antidote polypeptide of said proteic killer gene system that binds to said cytotoxin polypeptide, thereby acting as an antitoxin for said cytotoxin polypeptide; and (iii) cultivating said cell under conditions whereby the gene of said proteic killer gene system is expressed, and wherein a daughter cell that does not receive a copy of said extrachromosomal replicon is killed by said cytotoxin polypeptide in the absence of expression of said antidote polypeptide.