TIGHT REGULATION, MODULATION, AND HIGH-LEVEL EXPRESSION BY VECTORS CONTAINING THE ARABINOSE P-BAD PROMOTER

We have constructed a series of plasmid vectors (pBAD vectors) contain ing the P-BAD promoter of the araBAD (arabinose) operon and the gene e ncoding the positive and negative regulator of this promoter, araC. Us ing the phoA gene and phoA fusions to monitor expression in these vect ors, we show that the ratio of induction/repression can be 1,200-fold, compared with 50-fold for P-TAC-based vectors. phoA expression can be modulated over a wide range of inducer (arabinose) concentrations and reduced to extremely low levels by the presence of glucose, which rep resses expression. Also, the kinetics of induction and repression are very rapid and significantly affected by the ara allele in the host st rain. Thus, the use of this system which can be efficiently and rapidl y turned on and off allows the study of important aspects of bacterial physiology in a very simple manner and without changes of temperature . We have exploited the light regulation of the P-BAD promoter to stud y the phenotypes of null mutations of essential genes and explored the use of pBAD vectors as an expression system.