A theoretical steady state analysis indicates that induction of Escherichia coli glnALG operon can display all-or-none behavior
The nitrogen starvation response in Escherichia coli is characterized by the enhanced expression of Ntr regulon, comprising hundreds of genes including the one coding for nitrogen-assimilating glutamine synthetase (GS) enzyme. The biosynthesis and activity of GS is regulated mainly by nitrogen and carbon levels in the cell and monitored by three functionally separable interconnected modules. Here, we present the steady-state modular analysis of this intricate network made up of a GS bicyclic closed-loop cascade, a NRII-NRI two-component system, and an autoregulated glnALG operon encoding genes for GS, NRII, and NRI. Our simulation results indicate that the transcriptional output of glnALG operon is discrete and switch-like, whereas the activation of transcription factor NRI is graded, and the inactivation of GS is moderately ultrasensitive to input stimulus glutamine. The autoregulation of the NRII-NRI two-component system was found to be essential for the all-or-none induction of the glnALG operon. Furthermore, we show that the autoregulated two-component system modulates the total active GS by delineating the GS activity from its biosynthetic regulation. Our analysis indicates that the exclusive relationship between GS activity and its synthesis is brought about by the autoregulated two-component system. The modularity of the network endows the system to respond differently to nitrogen depending on the carbon status of the cell. Through a system-level quantification, we conclude that the discrete switch-like transcriptional response of the E. coli glnALG operon to nutrient starvation prevents the premature initiation of transcription and may represent the desperate attempt by the cell to survive in limiting conditions.
The authors have developed a mathematical model of regulation of expression of the Escherichia coli lac operon, and have investigated bistability in its steady-state induction behaviour in the absence of external glucose. Numerical analysis of equations describing regulation by artificial inducers revealed two natural bistability parameters that can be used to control the range of inducer conce...متن کامل
Regulation of kdp operon expression in Escherichia coli: evidence against turgor as signal for transcriptional control.
Kdp, an inducible high-affinity K+ transporter in Escherichia coli, is encoded by genes of the kdpABC operon, and its expression is regulated by the products of kdpD and kdpE. Loss of cell turgor has been proposed to be the signal which induces kdp expression (L. A. Laimins, D. B. Rhoads, and W. Epstein, Proc. Natl. Acad. Sci. USA 78:464-468, 1981). We reexamined kdp expression during steady-st...متن کامل
Background: Diarrhea caused by Escherichia coli is a major cause of morbidity and mortality in young animals. Few treatment options are available, mainly antibiotic therapy increasingly limited by resistance to commonly used drugs.Objectives: The aim of this work was to develop immunotherapy based on the use of camel VHH antibody fragments, or nanobodies,...متن کامل
Complex Nonlinear Behavior in Metabolic Processes: Global Bifurcation Analysis of Escherichia coli Growth on Multiple Substrates
The nonlinear behavior of metabolic systems can arise from at least two different sources. One comes from the nonlinear kinetics of chemical reactions in metabolism and the other from nonlinearity associated with regulatory processes. Consequently, organisms at a constant growth rate (as experienced in a chemostat) could display multiple metabolic states or display complex oscillatory behavior ...متن کامل
Controlled and functional expression of the Pseudomonas oleovorans alkane utilizing system in Pseudomonas putida and Escherichia coli.
The OCT plasmid encodes enzymes for alkane hydroxylation and alkanol dehydrogenation. Structural components are encoded on the 7.5-kilobase pair alkBAC operon, whereas positive regulatory components are encoded by alkR. We have constructed plasmids containing fusions of cloned alkBAC and alkR DNA and used these fusion plasmids to study the functional expression of the alkBAC operon and the regu...متن کامل