Genetic regulation of glycogen biosynthesis in Escherichia coli : In vivo effects of the catabolite repression and stringent response systems in glg gene expression

Abstract

The synthesis of two of the Escherichia coli glycogen biosynthetic enzymes, ADPglucose pyrophosphorylase ( glg C) and glycogen synthase ( glg A) was activated by the addition of 5 m M cyclic AMP (cAMP) to maxicells; synthesis of glycogen branching enzyme ( glg B) was unaffected. β -Galactosidase activity expressed from a gene fusion, φ(glg C- lac Z), was approximately five-fold higher in a cya + versus an isogenic cya − strain of E. coli . Addition of cAMP restored β -galactosidase in the cya − strain. The expression of φ(glg C‘−’ lac Z) encoded β -galactosidase activity in a series of spo T 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. The φ(glg C‘−’ lac Z) encoded β -galactosidase activity was also elevated three-to five-fold in strain AC70R1, which contains a transacting mutation ( glg Q) that affects the levels of the glycogen biosynthetic enzymes and glg C transcripts.