A novel inducible expression system for the functional study of toxic gene in bacteria.

The cloning and expression of toxic proteins in bacteria have posed a great challenge because of the leaky expression in inducible expression systems. Using artificial gene synthesis and clone screening methods, we identified a mutant T5 promoter, which significantly reduced leaky expression of lac operator. The mutant T5 promoter contains two T deletions at -35 region and may reduce promoter activity. A bacterial lethal gene, Φ174 lytic gene E, was successfully cloned in this system and expressed in the presence of isopropyl β-D-1-thiogalactopyranoside. The system is compatible with existing T5 inducible expression systems and can be used for the controlled expression of toxic proteins.