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 o f serine and the aromatic amino acids. A serC-aroA-lac translational f usion was constructed in the vector pMC1403. Synthesis of beta-galacto sidase from the serC-aroA-lac fusion was found to be enhanced in the p resence of lactose as the sole carbon source. This enhancement was not observed in strains containing a cya or crp mutant. However, the exog enous addition of cAMP greatly increased the beta-galactosidase synthe sis in the cya mutant strain. The serC-aroA mRNA content, analyzed by a dot blot assay, also appeared to increase in the serC(+) aroA(+) cel ls after the exogenous addition of cAMP. These findings unambiguously indicate that the expression of the serC-aroA operon is positively con trolled by cAMP.