EFFICIENCY OF THE PTF-FC2 PAS POISON-ANTIDOTE STABILITY SYSTEM IN ESCHERICHIA-COLI IS AFFECTED BY THE HOST STRAIN, AND ANTIDOTE DEGRADATIONREQUIRES THE LON PROTEASE

The stabilization of a test plasmid by the proteic, poison-antidote pl asmid addiction system (pas) of plasmid pTF-FC2 was host strain depend ent, with a 100-fold increase in stability in Escherichia call CSH50, a 2.5-fold increase in E. coli JM105, and no detectable stabilization in E. call strains JM107 and JM109. The lethality of the PasB toxin wa s far higher in the E. coli strains in which the pas was most effectiv e. Models for the way in which poison-antidote systems stabilize plasm ids require that the antidote have a much higher rate of turnover than that of the toxin. A decrease in host cell death following plasmid lo ss from an E. call ion mutant and a decrease in plasmid stability sugg ested that the Lon protease plays a role in the rate of turnover of Pa sA antidote.