147 research outputs found

    Regulation of the Escherichia coli HipBA Toxin-Antitoxin System by Proteolysis

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    Bacterial populations produce antibiotic-tolerant persister cells. A number of recent studies point to the involvement of toxin/antitoxin (TA) modules in persister formation. hipBA is a type II TA module that codes for the HipB antitoxin and the HipA toxin. HipA is an EF-Tu kinase, which causes protein synthesis inhibition and dormancy upon phosphorylation of its substrate. Antitoxins are labile proteins that are degraded by one of the cytosolic ATP-dependent proteases. We followed the rate of HipB degradation in different protease deficient strains and found that HipB was stabilized in a lon- background. These findings were confirmed in an in vitro degradation assay, showing that Lon is the main protease responsible for HipB proteolysis. Moreover, we demonstrated that degradation of HipB is dependent on the presence of an unstructured carboxy-terminal stretch of HipB that encompasses the last 16 amino acid residues. Further, substitution of the conserved carboxy-terminal tryptophan of HipB to alanine or even the complete removal of this 16 residue fragment did not alter the affinity of HipB for hipBA operator DNA or for HipA indicating that the major role of this region of HipB is to control HipB degradation and hence HipA-mediated persistence

    SOS Response Induces Persistence to Fluoroquinolones in Escherichia coli

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    Bacteria can survive antibiotic treatment without acquiring heritable antibiotic resistance. We investigated persistence to the fluoroquinolone ciprofloxacin in Escherichia coli. Our data show that a majority of persisters to ciprofloxacin were formed upon exposure to the antibiotic, in a manner dependent on the SOS gene network. These findings reveal an active and inducible mechanism of persister formation mediated by the SOS response, challenging the prevailing view that persisters are pre-existing and formed purely by stochastic means. SOS-induced persistence is a novel mechanism by which cells can counteract DNA damage and promote survival to fluoroquinolones. This unique survival mechanism may be an important factor influencing the outcome of antibiotic therapy in vivo

    Molecular cloning and expression of hipA, a gene of Escherichia coli K-12 that affects frequency of persistence after inhibition of murein synthesis.

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    The hipA gene at 33.8 min on the Escherichia coli chromosome controls the frequency of persistence upon inhibition of murein synthesis; for strains bearing hipA+ the frequency is 10(-6), and for hipA- strains the frequency is 10(-2). hip+ has been cloned by selection for a kanamycin resistance determinant at 33.9 min. hipA+ is dominant over hipA- in both recA+ and recA- backgrounds. The smallest DNA insert which contains hipA+, as determined by the ability of the plasmids to complement hipA- strains, is 1,885 base pairs. Both orientations of hipA+ are obtained when the cloning site of vector is remote from strong promoters; both orientations complement hipA-, and both encode a unique peptide of 50,000 Mr. The probable direction of transcription has been deduced from the pattern of peptides encoded by plasmids from which either end of the insert and adjacent vector sequences have been deleted. This information and the recovery of only one orientation of hipA+ when the cloning site is close to a strong promoter suggest that a high level of expression of the gene is not tolerated by E. coli

    3-Methyleneoxindole Reductase of Peas

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