Combinatorial stress responses: direct coupling of two major stress responses in Escherichia coli.

Daniel Brown,Martin Buck,Sivaramesh Wigneshweraraj,Zhensheng Pan,Geraint Barton

doi:10.15698/mic2014.09.168

Abstract

Nitrogen is an essential element for all life, and this is no different for the bacterial cell. Numerous cellular macromolecules contain nitrogen, including proteins, nucleic acids and cell wall components. In Escherichia coli and related bacteria, the nitrogen stress (Ntr) response allows cells to rapidly sense and adapt to nitrogen limitation by scavenging for alternative nitrogen sources through the transcriptional activation of transport systems and catabolic and biosynthetic operons by the global transcriptional regulator NtrC. Nitrogen-starved bacterial cells also synthesize the (p)ppGpp effector molecules of a second global bacterial stress response - the stringent response. Recently, we showed that the transcription of relA, the gene which encodes the major (p)ppGpp synthetase in E. coli, is activated by NtrC during nitrogen starvation. Our results revealed that in E. coli and related bacteria, NtrC functions in combinatorial stress and serves to couple two major stress responses, the Ntr response and stringent response.

Highlights

The synthesis of (p)ppGpp in response to nutritional stresses has been studied for more than forty years
The transcriptional inhibition of stable RNA synthesis has a knock-on effect of releasing the RNA polymerase (RNAp) from these highly transcribed genes and thereby allowing adaptive reprogramming of gene expression to cope with the stress
In response to nitrogen starvation, NtrC reprograms transcription by directly activating approximately 45 genes, which allows the expression of scavenging and transport systems for alternative nitrogen sources, genes that encode proteins involved in catabolism of nitrogenous com

Summary

Introduction

The synthesis of (p)ppGpp in response to nutritional stresses has been studied for more than forty years. In Escherichia coli and related bacteria, the nitrogen stress (Ntr) response allows cells to rapidly sense and adapt to nitrogen limitation by scavenging for alternative nitrogen sources through the transcriptional activation of transport systems and catabolic and biosynthetic operons by the global transcriptional regulator NtrC.

Results

Conclusion