A novel strategy for regulated expression of a cytotoxic gene.

The tetracycline (Tet) transactivator system is a powerful promoter system to control gene expression. However, expression of a cytotoxic gene in this system has been limited due to the lethal effect caused by low levels of basal expression of the toxic gene. In this report, we describe a novel strategy to express a toxic gene using the Tet system. The barstar gene is placed downstream of a minimal promoter and the barnase gene downstream of the tetracycline responsive element minimal promoter. When barnase is expressed at a basal level, its toxicity in human cell culture is offset by the similar basal level expression of barstar. However, when the barnase expression is induced with the transactivator protein, its overproduction leads to cell death. Therefore, this strategy allows cytotoxicity to be effectively regulated by tetracycline.