Genetic regulation of glycogen biosynthesis inEscherichia coli: In vivo effects of the catabolite repression and stringent response systems inglg gene expression
The synthesis of two of theEscherichia coli glycogen biosynthetic enzymes, ADPglucose pyrophosphorylase (glgC) and glycogen synthase (glgA) was activated by the addition of 5 mM cyclic AMP (cAMP) to maxicells; synthesis of glycogen branching enzyme (glgB) was unaffected.β-Galactosidase activity expressed from a gene fusion,φ(glgC-lacZ), was approximately five-fold higher in acya+ versus an isogeniccya− strain ofE. coli. Addition of cAMP restoredβ-galactosidase in thecya− strain. The expression ofφ(glgC‘−’lacZ) encodedβ-galactosidase activity in a series ofspoT mutants exhibited an apparent exponential relationship to intracellular guanosine 5′-diphosphate 3′-diphosphate (ppGpp) levels. These results provide evidence for the control of glycogen biosynthesis in vivo by cAMP and ppGpp at the level of gene expression, and identify a region of DNA required for the control. Theφ(glgC‘−’lacZ) encodedβ-galactosidase activity was also elevated three-to five-fold in strain AC70R1, which contains a transacting mutation (glgQ) that affects the levels of the glycogen biosynthetic enzymes andglgC transcripts.
KeywordsEnzyme Gene Expression Response System Diphosphate Gene Fusion
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