Wily Phage Trumps Host Toxin

摘要

Toxin-antitoxin (TA) systems are a dimea dozen. They are found on plasmidsand chromosomes within many pro-karyote groups—even those with anintracellular lifestyle. Each is a two-geneoperon, one gene encoding a toxin pro-tein, the other the cognate antitoxin.Key to their function is the differentialstability of the two gene products, theantitoxin degrading more rapidly thanthe toxin. When both the toxin and theantitoxin are present in the cell, all iswell. They interact and the antitoxinneutralizes the toxin. When productionis halted, the toxin outlives the antidoteand then kills the cell (or at least inhibitsits growth). TA systems carried on plas-mids have earned the epithet "addictionmodule." If a host cell jettisons the plas-mid, it is dead, thus guaranteeing themaintenance of the plasmid in the hostcell lineage.