Interaction in vivo between strong closely spaced constitutive promoters.

By genetic recombination procedures we have constructed strains of Escherichia coli K12 wherein up to three strong promoters ostensibly could function simultaneously and independently in the formation of messenger RNA molecules which specify tryptophan synthase. In all such multiple promoter cases, enzyme production falls short of the levels predicted from summing the measured contributions of each promoter taken singly. Possible molecular explanations for this phenomenon, which can produce apparent interferences in enzyme production as high as 42%, are considered.