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  • 1.
    Holmqvist, Erik
    et al.
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
    Unoson, Cecilia
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology.
    Reimegård, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Wagner, Gerhart E. H.
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
    A mixed double negative feedback loop between the sRNA MicF and the global regulator Lrp2012In: Molecular Microbiology, ISSN 0950-382X, E-ISSN 1365-2958, Vol. 84, no 3, p. 414-427Article in journal (Refereed)
    Abstract [en]

    Roughly 10% of all genes in Escherichia coli are controlled by the global transcription factor Lrp, which responds to nutrient availability. Bioinformatically, we identified lrp as one of several putative targets for the sRNA MicF, which is transcriptionally downregulated by Lrp. Deleting micF results in higher Lrp levels, while overexpression of MicF inhibits Lrp synthesis. This effect is by antisense; mutations in the predicted interaction region relieve MicF-dependent repression of Lrp synthesis, and regulation is restored by compensatory mutations. In vitro, MicF sterically interferes with initiation complex formation and inhibits lrp mRNA translation. In vivo, MicF indirectly activates genes in the Lrp regulon by repressing Lrp, and causes severely impaired growth in minimal medium, a phenotype characteristic of lrp deletion strains. The double negative feedback between MicF and Lrp may promote a switch for adequate Lrp-dependent adaptation to nutrient availability. Lrp adds to the growing list of transcription factors that are targeted by sRNAs, thus indicating that perhaps the majority of all bacterial genes may be directly or indirectly controlled by sRNAs.

  • 2.
    Holmqvist, Erik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
    Unoson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
    Reimegård, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
    Wagner, Gerhart E. H.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology.
    The sRNA MicF targets its own regulator Lrp and promotes a positive feedback loopManuscript (preprint) (Other academic)
    Abstract [en]

    As much as 10% of all genes in Escherichia coli are controlled by the global transcription factor Lrp, whose expression changes depending on the nutritional status of the environment. The output of Lrp regulation can be modulated by cellular leucine, which either enhances or reverses the effect on Lrp-targeted promoters. In a bioinformatic search for sRNA targets, lrp was identified as a putative target for the MicF sRNA, whose expression is negatively regulated by Lrp. A deletion of micF resulted in higher Lrp levels, while overexpression of MicF strongly inhibited Lrp expression. Mutations in the predicted interaction sequence of MicF and lrp relieved MicF-dependent repression of Lrp synthesis, both in vivo and in vitro. The predicted base-pairing interaction was supported by structural probing. Additionally, we show that MicF specifically interferes with initiating ribosomes on the lrp mRNA in vitro. In vivo, MicF-dependent inhibition of Lrp synthesis resulted in increased expression of the livJ gene, a member of the Lrp regulon. Finally, MicF was shown to increase its own expression through Lrp, creating a positive feedback loop. These findings contribute to the understanding of Lrp regulation in particular and the involvement of sRNAs in regulatory networks in general.

  • 3.
    Jones, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Leroy, Prune
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Systems Biology.
    Unoson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Microbiology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Fange, David
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Curic, Vladimir
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Lawson, Michael J.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Elf, Johan
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular Systems Biology. Uppsala Univ, Dept Cell & Mol Biol, Sci Life Lab, Uppsala, Sweden..
    Kinetics of dCas9 target search in Escherichia coli2017In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 357, no 6358, p. 1420-1423Article in journal (Refereed)
    Abstract [en]

    How fast can a cell locate a specific chromosomal DNA sequence specified by a single-stranded oligonucleotide? To address this question, we investigate the intracellular search processes of the Cas9 protein, which can be programmed by a guide RNA to bind essentially any DNA sequence. This targeting flexibility requires Cas9 to unwind the DNA double helix to test for correct base pairing to the guide RNA. Here we study the search mechanisms of the catalytically inactive Cas9 (dCas9) in living Escherichia coli by combining single-molecule fluorescence microscopy and bulk restriction-protection assays. We find that it takes a single fluorescently labeled dCas9 6 hours to find the correct target sequence, which implies that each potential target is bound for less than 30 milliseconds. Once bound, dCas9 remains associated until replication. To achieve fast targeting, both Cas9 and its guide RNA have to be present at high concentrations.

  • 4.
    Persson, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology.
    Linden, Martin
    Unoson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology.
    Elf, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology.
    A Bayesian Approach to Single Particle Tracking Analysis2013In: Biophysical Journal, ISSN 0006-3495, E-ISSN 1542-0086, Vol. 104, no 2, p. 177A-177AArticle in journal (Other academic)
  • 5.
    Persson, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Linden, Martin
    Unoson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Elf, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Extracting intracellular diffusive states and transition rates from single-molecule tracking data2013In: Nature Methods, ISSN 1548-7091, E-ISSN 1548-7105, Vol. 10, no 3, p. 265-269Article in journal (Refereed)
    Abstract [en]

    We provide an analytical tool based on a variational Bayesian treatment of hidden Markov models to combine the information from thousands of short single-molecule trajectories of intracellularly diffusing proteins. The method identifies the number of diffusive states and the state transition rates. Using this method we have created an objective interaction map for Hfq, a protein that mediates interactions between small regulatory RNAs and their mRNA targets.

  • 6.
    Wagner, Gerhart E. H.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Unoson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
    The toxin-antitoxin system tisB-istR1 Expression, regulation and biological role in persister phenotypes2012In: RNA Biology, ISSN 1547-6286, E-ISSN 1555-8584, Vol. 9, no 12, p. 1513-1519Article, review/survey (Refereed)
    Abstract [en]

    Chromosomally encoded toxin-antitoxin (TA) systems are abundantly present in bacteria and archaea. They have become a hot topic in recent years, because-after many frustrating years of searching for biological functions-some are now known to play roles in persister formation. Persisterscells represent a subset of a bacterial population that enters a dormant state and thus becomes refractory to the action of antibiotics. TA modules come in several different flavors, regarding the nature of their gene products, their molecular mechanisms of regulation, their cellular targets, and probably their role in physiology. This review will primarily focus on the SOS-associated tisB/istR1 system in Escherichia coli and discuss its nuts and bolts as well as its effect in promoting a subpopulation phenotype that likely benefits long-term survival of a stressed population.

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