The PhoP/PhoQ two-component system stabilizes the alternative sigma factor RpoS in Salmonella enterica

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125

117

IraP is a small protein that interferes with the delivery of S (RpoS) to the ClpXP protease by blocking the action of RssB, an adaptor protein for S degradation. IraP was previously shown to mediate stabilization of S during phosphate starvation. Here, we show that iraP is transcribed in response to phosphate starvation; this response is mediated by ppGpp. The iraP promoter is positively regulated by ppGpp, dependent on the discriminator region of the iraP promoter. Sensing of phosphate starvation requires SpoT but not RelA. The results demonstrate a target for positive regulation by ppGpp and suggest that the cell use of ppGpp to mediate a variety of starvation responses operates in part by modulating S levels.phosphate starvation ͉ 38 ͉ SpoT B acteria have evolved sophisticated mechanisms to recognize and respond to a variety of environmental stresses. In Escherichia coli, S , the gene product of rpoS, is the factor of the general stress response and adaptation to stationary phase (1, 2). S controls the expression of Ϸ100 genes involved in functions that help cells cope with various kinds of stress. S amounts and activity are tightly regulated (3-5).In exponentially growing cells, the active proteolysis of S is crucial to maintain a low intracellular concentration of this factor (6, 7). S becomes stable as cells are starved or are exposed to certain stresses (reviewed in ref. 4). S protein turnover requires the energy-dependent protease, ClpXP, and the adaptor protein, RssB (SprE), which binds directly to S and targets it to ClpXP (8). RssB has an N-terminal domain of the response regulator family, with a conserved site for phosphorylation. Recently, the identification of an anti-adaptor protein, IraP, provided an explanation for how proteolysis of S can be regulated. In vivo, S is stabilized after phosphate starvation in a manner that depends on IraP and that is independent of RssB phosphorylation. In vitro, IraP inhibits S proteolysis through a direct interaction with RssB (9). Although the inhibitory effect of IraP on S degradation has been observed in response to phosphate starvation, how phosphate starvation is sensed and how this signal affects IraP expression and/or activity has not been described previously. We show in this work that iraP mRNA accumulates in phosphate-starved cells, dependent on the alarmone ppGpp, the global regulator of the stringent response. This induction requires the discriminator sequence of the iraP promoter. Two proteins in E. coli, RelA and SpoT, are capable of synthesizing ppGpp (10, 11); we find that SpoT, but not RelA, is essential for the induction of iraP expression in response to phosphate starvation. The positive regulation of iraP transcription by ppGpp leads to regulation of S proteolysis.Results iraP mRNA Accumulates in Response to Phosphate Starvation. Previous work showed that IraP stabilizes the transcription factor S under phosphate starvation (9). We analyzed by Northern blot the levels of iraP mRNA before and after removal of phosphate. Fig. 1A shows that iraP...

Section: Discussion Ppgpp Activation Of Irap Transcription Results Inmentioning

confidence: 60%

ppGpp regulation of RpoS degradation via anti-adaptor protein IraP

Bougdour

Gottesman

2007

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125

117

“…To uncover the genes directly regulated by PhoP in Y. pestis, we used a combination of expression microarray analysis (wild-type vs. phoP mutant strains) and ChIP followed by array hybridization (ChIP-chip). S1 mapping (43), primer extension (44), and DNase I footprinting (43) experiments were used to validate the microarray and ChIP-chip results and to determine the structure of the PhoP-activated promoters described in Fig. 3B.…”

Section: Methodsmentioning

confidence: 99%

Transcription factor function and promoter architecture govern the evolution of bacterial regulons

Pérez

Groisman

2009

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Evolutionary changes in ancestral regulatory circuits can bring about phenotypic differences between related organisms. Studies of regulatory circuits in eukaryotes suggest that these modifications result primarily from changes in cis-regulatory elements (as opposed to alterations in the transcription factors that act upon these sequences). It is presently unclear how the evolution of gene regulatory circuits has proceeded in bacteria, given the rampant effects of horizontal gene transfer, which has significantly altered the composition of bacterial regulons. We now demonstrate that the evolution of the regulons governed by the regulatory protein PhoP in the related human pathogens Salmonella enterica and Yersinia pestis has entailed functional changes in the PhoP protein as well as in the architecture of PhoP-dependent promoters. These changes have resulted in orthologous PhoP proteins that differ both in their ability to promote transcription and in their role as virulence regulators. We posit that these changes allow bacterial transcription factors to incorporate newly acquired genes into ancestral regulatory circuits and yet retain control of the core members of a regulon.cis-regulatory elements ͉ horizontal gene transfer ͉ PhoP ͉ Salmonella ͉ Yersinia

“…Despite recent progress in the description and characterization of network motifs (1), there is still limited knowledge about the quantitative behavior of different regulatory designs even for well studied microorganisms. Here, we explore a regulatory design that relies on a class of bacterial proteins, termed connectors, that have the unique property of connecting two-component systems (2)(3)(4)(5), which constitute the most prevalent form of bacterial signal transduction (6,7).…”

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confidence: 99%

A connector of two-component regulatory systems promotes signal amplification and persistence of expression

Kato

Mitrophanov²,

Groisman³

2007

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Organisms rely on a variety of regulatory architectures to control gene transcription. Whereas the functional characteristics of particular architectures are well understood, the properties of newly discovered regulatory designs cannot be easily predicted. One emerging design depends on small proteins that connect twocomponent regulatory systems, which constitute the dominant form of bacterial signal transduction. These connectors enable one system to respond to the signal perceived by a different system. To understand the functional properties of such connector-mediated architectures, we investigated the pathway controlled by the PhoP-dependent connector protein PmrD of Salmonella enterica and contrasted it to the circuit in which genes are regulated directly by the transcription factor PhoP. The PmrD-mediated pathway displayed both signal amplification and persistence of expression when compared with the direct pathway. Mathematical modeling of the two pathways allowed us to identify critical factors responsible for signal amplification. mathematical modeling ͉ Salmonella ͉ signal transduction ͉ transcriptional regulatory circuit ͉ two-component system