Regulation of P-Galactosidase Synthesis in Escherichia coli by Cyclic Adenosine 3’, 5’-Monophosphate

Cyclic adenosine 3’,5’-monophosphate (cyclic AMP) increases the differential rate of synthesis of @-galactosidase in Escherichia coli made permeable by treatment with t&(hydroxymethyl)aminomethane and ethylenediaminetetraacetic acid. In normal, growing cells, cyclic AMP overcomes the transient repression of /3-galactosidase by glucose. A half-maximal effect of cyclic AMP occurs at about 7 x 10-S rd. Cyclic AMP overcomes the transient repression of P-galactosidase synthesis in two regulatory mutants which produce @-galactosidase constitutively, 3300 (i-) and O&. Cyclic AMP also acts in cells which are deficient in the lac permease. Cyclic AMP overcomes the transient repression of pgalactosidase synthesis produced by cr-methylglucoside in strain C600 which has normal regulatory genes. In mutant LA-12G, which is resistant to permanent repression, cyclic AMP also overcomes transient glucose repression. In cells treated with chloramphenicol, isopropylthio-P-Dgalactopyranoside promotes the accumulation of P-galactosidase-specific messenger RNA, glucose prevents its accumulation, and cyclic AMP overcomes this repression by glucose. Cyclic AMP also overcomes the glucose repression of mRNA production in a threonine-requiring mutant during threonine starvation. Cyclic AMP fails to stimulate @-galactosidase production in cells in which mRNA synthesis has been arrested by inducer removal or proflavine addition. Thus, cyclic AMP appears to participate in the regulation of bgalactosidase mRNA synthesis at the gene level. thesizing the enzyme (1). This phenomenon has been called the glucose effect (2), catabolite repression (3), or metabolic repression (4). Nakada and Magasanik (5) have investigated the mechanism of catabolite repression and found that glucose repressed the synthesis of messenger RNA specific for P-galactosidase. In a preliminary communication (6), we reported that the synthesis of ,&galactosidase is stimulated and its repression by glucose prevented by cyclic AMP.I Thjs effect of cyclic AMP is specific inasmuch as ATP, ADP, 3’-AMP, 5’-AMP, adenosine, adenine, and fructose 1,6-diphosphate were inactive. Further, cyclic AMP failed to affect the over-all rate of protein or RNA synthesis; thus, it increased the differential rate of @galactosidase synthesis. In this paper, the effect of cyclic AMP on /3-galactosidase synthesis has been further characterized. In addition, we show that cyclic AMP act,s at the level at which DNA is transcribed into RNA.