Adenosine 3':5'-cyclic monophosphate as mediator of catabolite repression in Escherichia coli

Measurements of intracellular adenosine 3':5'-cyclic monophosphate (cAMP) concentrations in E. coli under a variety of conditions show that levels of this nucleotide are well correlated with the rate of synthesis of beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) in both catabolite repression and transient repression. These results, combined with extensive genetic and in vitro studies from a number of laboratories on the role of cAMP in E. coli, provide strong support for the concept that intracellular cAMP levels mediate the effects of catabolite and transient repression on rates on enzyme synthesis. Under all conditions studied, excretion can be described by a single rate constant, 2.1 min-1 at 37 degrees, indicating that intracellular levels cannot be regulated by alterations in the rate of cAMP excretion. Our data are fully consistent with the idea that carbon sources control intracellular cAMP levels by effects on its synthesis.