PMID:7494474
| Citation |
Tagami, H, Inada, T, Kunimura, T and Aiba, H (1995) Glucose lowers CRP* levels resulting in repression of the lac operon in cells lacking cAMP. Mol. Microbiol. 17:251-8 |
|---|---|
| Abstract |
CRP-cAMP-dependent operons of Escherichia coli can be expressed in cells lacking functional adenylate cyclase when they carry a second-site mutation in the crp gene (crp*). It is known that the expression of these operons is repressed by glucose, but the molecular mechanism underlying this cAMP-independent catabolite repression has been a long-standing mystery. Here we address the question of how glucose inhibits the expression of beta-galactosidase in the absence of cAMP. We have isolated several mutations in the crp gene that confer a CRP* phenotype. The expression of beta-galactosidase is reduced by glucose in cells carrying these mutations. Using Western blotting and/or SDS-PAGE analysis, we demonstrate that glucose lowers the cellular concentration of CRP* through a reduction in crp* mRNA levels. The level of CRP* protein correlates with beta-galactosidase activity. When the crp promoter is replaced with the bla promoter, the inhibitory effect of glucose on crp* expression is virtually abolished. These data strongly suggest that the lowered level of CRP* caused by glucose mediates catabolite repression in cya- crp* cells and that the autoregulatory circuit of the crp gene is involved in the down-regulation of CRP* expression by glucose. |
| Links | |
| Keywords |
Adenylate Cyclase/physiology; Carrier Proteins; Cyclic AMP/metabolism; Cyclic AMP Receptor Protein/biosynthesis; Cyclic AMP Receptor Protein/genetics; Enzyme Repression; Escherichia coli/enzymology; Escherichia coli/genetics; Gene Amplification; Gene Expression Regulation, Bacterial/drug effects; Genes, Bacterial; Glucose/pharmacology; Lac Operon/genetics; Plasmids/genetics; Point Mutation; Promoter Regions, Genetic/genetics; RNA, Bacterial/biosynthesis; RNA, Messenger/biosynthesis; beta-Galactosidase/biosynthesis; beta-Galactosidase/metabolism |
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