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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 21 April 2015, Vol.112(16), pp.5159-64
    Description: RpoS, the stationary phase/stress sigma factor of Escherichia coli, regulates a large cohort of genes important for the cell to deal with suboptimal conditions. Its level increases quickly in the cell in response to many stresses and returns to low levels when growth resumes. Increased RpoS results from increased translation and decreased RpoS degradation. Translation is positively regulated by small RNAs (sRNAs). Protein stability is positively regulated by anti-adaptors, which prevent the RssB adaptor-mediated degradation of RpoS by the ClpXP protease. Inactivation of aceE, a subunit of pyruvate dehydrogenase (PDH), was found to increase levels of RpoS by affecting both translation and protein degradation. The stabilization of RpoS in aceE mutants is dependent on increased transcription and translation of IraP and IraD, two known anti-adaptors. The aceE mutation also leads to a significant increase in rpoS translation. The sRNAs known to positively regulate RpoS are not responsible for the increased translation; sequences around the start codon are sufficient for the induction of translation. PDH synthesizes acetyl-CoA; acetate supplementation allows the cell to synthesize acetyl-CoA by an alternative, less favored pathway, in part dependent upon RpoS. Acetate addition suppressed the effects of the aceE mutant on induction of the anti-adaptors, RpoS stabilization, and rpoS translation. Thus, the bacterial cell responds to lowered levels of acetyl-CoA by inducing RpoS, allowing reprogramming of E. coli metabolism.
    Keywords: Clpxp ; Rpos ; Rssb ; Acetyl Coa ; Pyruvate Dehydrogenase ; Protein Biosynthesis ; Proteolysis ; Stress, Physiological ; Bacterial Proteins -- Metabolism ; Escherichia Coli -- Metabolism ; Sigma Factor -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 8 June 2010, Vol.107(23), pp.10691-10695
    Description: Perception and response to nutritional iron availability by bacteria are essential to control cellular iron homeostasis. The Irr protein from Bradyrhizobium japonicum senses iron through the status of heme biosynthesis to globally regulate iron-dependent gene expression. Heme binds directly to Irr to trigger its degradation. Here, we show that severe manganese limitation created by growth of a Mn²⁺ transport mutant in manganese-limited media resulted in a cellular iron deficiency. In wild-type cells, Irr levels were attenuated under manganese limitation, resulting in reduced promoter occupancy of target genes and altered iron-dependent gene expression. Irr levels were high regardless of manganese availability in a heme-deficient mutant, indicating that manganese normally affects heme-dependent degradation of Irr. Manganese altered the secondary structure of Irr in vitro and inhibited binding of heme to the protein. We propose that manganese limitation destabilizes Irr under low-iron conditions by lowering the threshold of heme that can trigger Irr degradation. The findings implicate a mechanism for the control of iron homeostasis by manganese in a bacterium.
    Keywords: Physical sciences -- Chemistry -- Chemical elements ; Physical sciences -- Chemistry -- Chemical elements ; Biological sciences -- Biology -- Genetics ; Physical sciences -- Chemistry -- Chemical compounds ; Biological sciences -- Biology -- Genetics ; Biological sciences -- Biology -- Microbiology ; Biological sciences -- Biology -- Cytology ; Biological sciences -- Biology -- Physiology ; Biological sciences -- Biochemistry -- Metabolism ; Biological sciences -- Biology -- Physiology
    ISSN: 00278424
    E-ISSN: 10916490
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  • 3
    Language: English
    In: Nucleic acids research, 19 August 2016, Vol.44(14), pp.6907-23
    Description: Post-transcriptional regulation of transcription factors contributes to regulatory circuits. We created translational reporter fusions for multiple central regulators in Escherichia coli and examined the effect of Hfq-dependent non-coding RNAs on these fusions. This approach yields an 'RNA landscape,' identifying Hfq-dependent sRNAs that regulate a given fusion. No significant sRNA regulation of crp or fnr was detected. hns was regulated only by DsrA, as previously reported. Lrp and SoxS were both found to be regulated post-transcriptionally. Lrp, ' L: eucine-responsive R: egulatory P: rotein,' regulates genes involved in amino acid biosynthesis and catabolism and other cellular functions. sRNAs DsrA, MicF and GcvB each independently downregulate the lrp translational fusion, confirming previous reports for MicF and GcvB. MicF and DsrA interact with an overlapping site early in the lrp ORF, while GcvB acts upstream at two independent sites in the long lrp leader. Surprisingly, GcvB was found to be responsible for significant downregulation of lrp after oxidative stress; MicF also contributed. SoxS, an activator of genes used to combat oxidative stress, is negatively regulated by sRNA MgrR. This study demonstrates that while not all global regulators are subject to sRNA regulation, post-transcriptional control by sRNAs allows multiple environmental signals to affect synthesis of the transcriptional regulator.
    Keywords: Gene Expression Regulation, Bacterial ; Transcription, Genetic ; Escherichia Coli -- Genetics ; Escherichia Coli Proteins -- Genetics ; Leucine-Responsive Regulatory Protein -- Genetics ; RNA, Bacterial -- Metabolism ; Trans-Activators -- Genetics
    ISSN: 03051048
    E-ISSN: 1362-4962
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  • 4
    In: Molecular Microbiology, November 2012, Vol.86(3), pp.524-538
    Description: Small ‐dependent non‐coding regulatory s (s) that alter stability and expression by pairing with target s have increasingly been shown to be important in influencing the behaviour of bacteria. In , and , which encode the master regulator of flagellar synthesis, are co‐transcribed from a promoter that is regulated by multiple transcription factors that respond to different environmental cues. Here, we show that the 5′ untranslated region (5′ ) of the also serves as a hub to integrate additional environmental cues into the decision to make flagella. Four s, , , and , negatively regulated and one , , positively regulated motility and expression by base‐pairing with the 5′ of this . Another , , positively regulated motility independent of regulation of . Furthermore, we demonstrate that the regulation of motility by the / two component system is in part due to its regulation of . is the first that has been shown to be both positively and negatively regulated by direct pairing to s. Moreover, both positive regulation by and negative regulation by require the same binding site in the .
    Keywords: Biology;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 5
    Language: English
    In: The Journal of Bacteriology, 2010, Vol. 192(21), p.5559
    Description: Small noncoding RNAs (sRNAs) regulate gene expression in Escherichia coli by base pairing with mRNAs and modulating translation and mRNA stability. The sRNAs DsrA and RprA stimulate the translation of the stress response transcription factor RpoS by base pairing with the 5' untranslated region of the rpoS mRNA. In the present study, we found that the rpoS mRNA was unstable in the absence of DsrA and RprA and that expression of these sRNAs increased both the accumulation and the half-life of the rpoS mRNA. Mutations in dsrA, rprA, or rpoS that disrupt the predicted pairing sequences and reduce translation of RpoS also destabilize the rpoS mRNA. We found that the rpoS mRNA accumulates in an RNase E mutant strain in the absence of sRNA expression and, therefore, is degraded by an RNase E-mediated mechanism. DsrA expression is required, however, for maximal translation even when rpoS mRNA is abundant. This suggests that DsrA protects rpoS mRNA from degradation by RNase E and that DsrA has a further activity in stimulating RpoS protein synthesis, rpoS mRNA is subject to degradation by an additional pathway, mediated by RNase III, which, in contrast to the RNase E-mediated pathway, occurs in the presence and absence of DsrA or RprA. rpoS mRNA and RpoS protein levels are increased in an RNase III mutant strain with or without the sRNAs, suggesting that the role of RNase III in this context is to reduce the translation of RpoS even when the sRNAs are acting to stimulate translation. doi: 10.1128/JB.00464-10
    Keywords: Messenger Rna -- Properties ; Protein Synthesis -- Research ; Bacterial Genetics -- Research ; Translation (Genetics) -- Research ; Escherichia Coli -- Genetic Aspects;
    ISSN: 0021-9193
    ISSN: 00219193
    E-ISSN: 10985530
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  • 6
    In: The Journal of Bacteriology, 2006, Vol. 188(19), p.7022
    Description: Regulated degradation of RpoS requires RssB and ClpXP protease. Mutations in hns increase both RpoS synthesis and stability, causing a twofold increase in synthesis and almost complete stabilization of RpoS, independent of effects on synthesis and independent of phosphorylation of RssB. This suggests that H-NS regulates an RssB inhibitor or inhibitors. [PUBLICATION ]
    Keywords: Chemical Synthesis ; Mutation ; Bacteriology;
    ISSN: 0021-9193
    ISSN: 00219193
    E-ISSN: 10985530
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  • 7
    In: The Journal of Bacteriology, 2007, Vol. 189(6), p.2238
    Description: SgrR is the first characterized member of a family of bacterial transcription factors containing an N-terminal DNA binding domain and a C-terminal solute binding domain. Previously, we reported genetic evidence that SgrR activates the divergently transcribed gene sgrS, which encodes a small RNA required for recovery from glucose-phosphate stress. In this study, we examined the regulation of sgrR expression and found that SgrR negatively autoregulates its own transcription in the presence and absence of stress. An SgrR binding site in the sgrR-sgrS intergenic region is required in vivo for both SgrR-dependent activation of sgrS and autorepression of sgrR. Purified SgrR binds specifically to sgrS promoter DNA in vitro; a mutation in the site required for in vivo activation and autorepression abrogates in vitro SgrR binding. A plasmid library screen identified clones that alter expression of a P sub(sgrS)-lacZ fusion; some act by titrating endogenous SgrR. The yfdZ gene, encoding a putative aminotransferase, was identified in this screen; the yfdZ promoter contains an SgrR binding site, and transcriptional fusions indicate that yfdZ is activated by SgrR. Clones containing mlc, which encodes a glucose-specific repressor protein, also downregulate P sub(sgrS)-lacZ. The mlc clones do not appear to titrate the SgrR protein, indicating that Mlc affects sgrS expression by an alternative mechanism.
    Keywords: Solutes ; Promoters ; RNA ; Transcription Factors ; DNA ; Stress ; Plasmids ; Mutation ; Repressors ; Gene Regulation ; Genetics & Taxonomy;
    ISSN: 0021-9193
    ISSN: 00219193
    E-ISSN: 10985530
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  • 8
    In: The Journal of Bacteriology, 1998, Vol. 180(5), p.1154
    Description: RpoS, the stationary-phase sigma factor of Escherichia coli, is responsible for increased transcription of an array of genes when cells enter stationary phase and under certain stress conditions. RpoS is rapidly degraded during exponential phase and much more slowly during stationary phase; the resulting changes in RpoS accumulation play an important role in providing differential expression of RpoS-dependent gene expression. It has previously been shown that rapid degradation of RpoS during exponential growth depends on RssB (also called SprE and MviA), a protein with homology to the family of response regulators, and on the ClpXP protease. We find that RssB regulation of proteolysis does not extend to another ClpXP substrate, bacteriophage lambda O protein, suggesting that RssB acts on the specific substrate RpoS rather than on the protease. In addition, the activity of RpoS is down-regulated by RssB when degradation is blocked. In cells blocked for RpoS degradation by a mutation in clpP, cells devoid of RssB show a four- to fivefold-higher activity of an RpoS-dependent reporter fusion than cells overproducing RssB. Therefore, RssB allows specific environmental regulation of RpoS accumulation and may also modulate activity. The regulation of degradation provides an irreversible switch, while the regulation of activity may provide a second, presumably reversible level of control.
    Keywords: DNA-Binding Proteins ; Escherichia Coli Proteins ; Transcription Factors ; Bacterial Proteins -- Metabolism ; Escherichia Coli -- Metabolism ; Sigma Factor -- Metabolism;
    ISSN: 0021-9193
    ISSN: 00219193
    E-ISSN: 10985530
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  • 9
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 15 January 2019, Vol.116(3), pp.1043-1052
    Description: Bacterial regulatory small RNAs act as crucial regulators in central carbon metabolism by modulating translation initiation and degradation of target mRNAs in metabolic pathways. Here, we demonstrate that a noncoding small RNA, SdhX, is produced by RNase E-dependent processing from the 3'UTR of the operon, encoding enzymes of the tricarboxylic acid (TCA) cycle. In , SdhX negatively regulates , which encodes an enzyme critical for degradation of the signaling molecule acetyl phosphate, while the downstream gene, encoding the enzyme critical for acetyl phosphate synthesis, is not significantly affected. This discoordinate regulation of and increases the accumulation of acetyl phosphate when SdhX is expressed. Mutations in that abolish regulation of lead to more acetate in the medium (more overflow metabolism), as well as a strong growth defect in the presence of acetate as sole carbon source, when the AckA-Pta pathway runs in reverse. SdhX overproduction confers resistance to hydroxyurea, via regulation of SdhX abundance is tightly coupled to the transcription signals of TCA cycle genes but escapes all known posttranscriptional regulation. Therefore, SdhX expression directly correlates with transcriptional input to the TCA cycle, providing an effective mechanism for the cell to link the TCA cycle with acetate metabolism pathways.
    Keywords: Hfq ; Rybd ; Acetate Kinase ; Acetyl-Phosphate ; Hydroxyurea ; Acetates -- Metabolism ; Citric Acid Cycle -- Physiology ; Escherichia Coli K12 -- Metabolism ; Escherichia Coli Proteins -- Metabolism ; RNA, Bacterial -- Metabolism ; RNA, Small Untranslated -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 10
    Language: English
    In: mBio, 10/31/2014, Vol.5(5)
    Description: UNLABELLED: How the architecture of DNA binding sites dictates the extent of repression of promoters is not well understood. Here, we addressed the importance of the number and information content of the three direct repeats (DRs) in the binding and repression of the icdA promoter by the phosphorylated form of the global Escherichia coli repressor ArcA (ArcA-P). We show that decreasing the information content of the two sites with the highest information (DR1 and DR2) eliminated ArcA binding to all three DRs and ArcA repression of icdA. Unexpectedly, we also found that DR3 occupancy functions principally in repression, since mutation of this low-information-content site both eliminated DNA binding to DR3 and significantly weakened icdA repression, despite the fact that binding to DR1 and DR2 was intact. In addition, increasing the information content of any one of the three DRs or addition of a fourth DR increased ArcA-dependent repression but perturbed signal-dependent regulation of repression. Thus, our data show that the information content and number of DR elements are critical architectural features for maintaining a balance between high-affinity binding and signal-dependent regulation of icdA promoter function in response to changes in ArcA-P levels. Optimization of such architectural features may be a common strategy to either dampen or enhance the sensitivity of DNA binding among the members of the large OmpR/PhoB family of regulators as well as other transcription factors.IMPORTANCE: In Escherichia coli, the response regulator ArcA maintains homeostasis of redox carriers under O2-limiting conditions through a comprehensive repression of carbon oxidation pathways that require aerobic respiration to recycle redox carriers. Although a binding site architecture comprised of a variable number of sequence recognition elements has been identified within the promoter regions of ArcA-repressed operons, it is unclear how this variable architecture dictates transcriptional regulation. By dissecting the role of multiple sequence elements within the icdA promoter, we provide insight into the design principles that allow ArcA to repress transcription within diverse promoter contexts. Our data suggest that the arrangement of recognition elements is tailored to achieve sufficient repression of a given promoter while maintaining appropriate signal-dependent regulation of repression, providing insight into how diverse binding site architectures link changes in O2 with the fine-tuning of carbon oxidation pathway levels.
    Keywords: Biology;
    ISSN: mBio
    E-ISSN: 2150-7511
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