Controlled expression in Klebsiella pneumoniae and Shigella flexneri usinga bacteriophage P1-derived C1-regulated promoter system

The utility of promoters regulated by the bacteriophage P1 temperature-sens itive Cl repressor was examined in Shigella flexneri and Klebsiella pneumon iae. Promoters carrying C1 operator sites driving LacZ expression had induc tion/repression ratios of up to 240-fold in S. flexneri and up to 50-fold i n K. pneumoniae. The promoters exhibited remarkably low basal expression, d emonstrated modulation by temperature, and showed rapid induction. This sys tem will provide a new opportunity for controlled gene expression in enteri c gram-negative bacteria.