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Co-ordinated regulation of the extracytoplasmic stress factor, sigmaE, with other Escherichia coli sigma factors by (p)ppGpp and DksA may be achieved by specific regulation of individual holoenzymes.

ABSTRACT: The E. coli alternative sigma factor, ?(E) , transcribes genes required to maintain the cell envelope and is activated by conditions that destabilize the envelope. ?(E) is also activated during entry into stationary phase in the absence of envelope stress by the alarmone (p)ppGpp. (p)ppGpp controls a large regulatory network, reducing expression of ?(70) -dependent genes required for rapid growth and activating ?(70) -dependent and alternative sigma factor-dependent genes required for stress survival. The DksA protein often potentiates the effects of (p)ppGpp. Here we examine regulation of ?(E) by (p)ppGpp and DksA following starvation for nutrients. We find that (p)ppGpp is required for increased ?(E) activity under all conditions tested, but the requirement for DksA varies. DksA is required during amino acid starvation, but is dispensable during phosphate starvation. In contrast, regulation of ?(S) is (p)ppGpp- and DksA-dependent under all conditions tested, while negative regulation of ?(70) is DksA- but not (p)ppGpp-dependent during phosphate starvation, yet requires both factors during amino acid starvation. These findings suggest that the mechanism of transcriptional regulation by (p)ppGpp and/or DksA cannot yet be explained by a unifying model and is specific to individual promoters, individual holoenzymes, and specific starvation conditions.

SUBMITTER: Gopalkrishnan S

PROVIDER: S-EPMC4497380 | biostudies-literature | 2014 Aug

REPOSITORIES: biostudies-literature

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Co-ordinated regulation of the extracytoplasmic stress factor, sigmaE, with other Escherichia coli sigma factors by (p)ppGpp and DksA may be achieved by specific regulation of individual holoenzymes.

Gopalkrishnan Saumya S Nicoloff Herve H Ades Sarah E SE

Molecular microbiology 20140710 3

The E. coli alternative sigma factor, σ(E) , transcribes genes required to maintain the cell envelope and is activated by conditions that destabilize the envelope. σ(E) is also activated during entry into stationary phase in the absence of envelope stress by the alarmone (p)ppGpp. (p)ppGpp controls a large regulatory network, reducing expression of σ(70) -dependent genes required for rapid growth and activating σ(70) -dependent and alternative sigma factor-dependent genes required for stress sur ...[more]

PMID: 24946009

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Project description:Salmonella enterica serovar Typhimurium (S. Typhimurium) elicits the starvation-stress response (SSR) due to starvation for an essential nutrient, e.g. a carbon/energy source (C-source). As part of the SSR, the alternative sigma factor sigma(E) is activated and induced. The authors suspect that this activation is, in part, triggered by changes in the S. Typhimurium cell envelope occurring during the adaptation from growth to carbon/energy starvation (C-starvation), and resulting in an increased need for sigma(E)-regulated factors involved in the proper folding and assembly of newly synthesized proteins destined for this extracytoplasmic compartment. This led to the hypothesis that a sigma(E) activation signal might arise during C-source shifts that cause the induction of proteins localized to the extracytoplasmic compartment, i.e. the outer membrane or periplasm, of the cell. To test this hypothesis, cultures were grown in minimal medium containing enough glucose to reach mid-exponential-phase, plus a non-limiting amount of a secondary 'less-preferred' but utilizable carbon/energy source. The sigma(E) activity was then monitored using plasmids carrying rpoEP1- and rpoEP2-lacZ transcriptional fusions, which exhibit sigma(E)-independent and -dependent lacZ expression, respectively. The secondary C-sources maltose, succinate and citrate, which have extracytoplasmic components involved in their utilization (e.g. LamB), resulted in a discernible diauxic lag period and a sustained increase in sigma(E) activity. Growth transition from glucose to other utilizable phosphotransferase (PTS) and non-PTS C-sources, such as trehalose, mannose, mannitol, fructose, glycerol, d-galactose or l-arabinose, did not cause a discernible diauxic lag period or a sustained increase in sigma(E) activity. Interestingly, a shift from glucose to melibiose, which does not use an extracytoplasmic-localized protein for uptake, did cause an observable diauxic lag period but did not result in a sustained increase in sigma(E) activity. In addition, overexpression of LamB from an arabinose-inducible promoter leads to a significant increase in sigma(E) activity in the absence of a glucose to maltose shift or C-starvation. Furthermore, a DeltalamB : : Omega-Km(r) mutant, lacking the LamB maltoporin, exhibited an approximately twofold reduction in the sustained sigma(E) activity observed during a glucose to maltose shift, again supporting the hypothesis. Interestingly, the LamB protein lacks the typical Y-X-F terminal tripeptide of the OmpC-like peptides that activate DegS protease activity leading to sigma(E) activation. It does, however, possess a terminal pentapeptide (Q-M-E-I-W-W) that may function as a ligand for a putative class II PDZ-binding site. The authors therefore propose that the sigma(E) regulon of S. Typhimurium not only is induced in response to deleterious environmental conditions, but also plays a role in the adaptation of cells to new growth conditions that necessitate changes in the extracytoplasmic compartment of the cell, which may involve alternative signal recognition and activation pathways that are independent of DegS.

Dataset Information

Co-ordinated regulation of the extracytoplasmic stress factor, sigmaE, with other Escherichia coli sigma factors by (p)ppGpp and DksA may be achieved by specific regulation of individual holoenzymes.

Publications

Co-ordinated regulation of the extracytoplasmic stress factor, sigmaE, with other Escherichia coli sigma factors by (p)ppGpp and DksA may be achieved by specific regulation of individual holoenzymes.

Similar Datasets

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