Autoregulation of the pTF-FC2 Proteic Poison-Antidote Plasmid Addiction System (pas) Is Essential for Plasmid Stabilization

The pasABC genes of the proteic plasmid addiction system of broad-host-range plasmid pTF-FC2 were autoregulated. The PasA antidote was able to repress the operon 25-fold on its own, and repression was increased to 100-fold when the PasB toxin was also present. Autoregulation appears to be an essential requirement for pas-mediated plasmid stabilization because when the pas genes were placed behind the isopropyl-β-d-thiogalactopyranoside (IPTG)-regulated tac promoter, they were unable to stabilize a heterologous test plasmid.