Expression of the Escherichia coli thioredoxin gene is negatively regulated by cyclic AMP

Regulation of the Escherichia coli thioredoxin gene (trxA) was studied using trxA-lac translational fusion constructed in the vector pMC1403. Synthesis of beta-galactosidase from the trxA-lac fusion was found to be repressed in the presence of lactose. A switch of carbon source from glucose to lactose and an addition of cyclic AMP (cAMP) caused a decrease in beta-galactosidase synthesis from the trxA-lac fusion. The repression effect of exogenous cAMP was not observed in the crp mutant strain. The beta-galactosidase synthesis from the trxA-lac fusion lacking a plausible cAMP-CRP binding site was not lowered in the presence of lactose or in the addition of cAMP. Expression of the chromosomal trxA gene was reduced by exogenous cAMP. These findings indicate that the expression of the trxA gene is controlled by cAMP in a negative manner.