Cyclic AMP-dependent expression of the Escherichia coli serC-aroA operon

The Escherichia coli serC-aroA operon encodes biosynthetic enzymes for unrelated amino acid biosynthetic pathways leading to the synthesis of serine and the aromatic amino acids. A serC-aroA-lac translational fusion was constructed in the vector pMC1403. Synthesis of beta-galactosidase from the serC-aroA-lac fusion was found to be enhanced in the presence of lactose as the sole carbon source. This enhancement was not observed in strains containing a cya or crp mutant. However, the exogenous addition of cAMP greatly increased the beta-galactosidase synthesis in the cya mutant strain. The serC-aroA mRNA content, analyzed by a dot blot assay, also appeared to increase in the serC+ aroA+ cells after the exogenous addition of cAMP. These findings unambiguously indicate that the expression of the serC-aroA operon is positively controlled by cAMP.