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  • Blackwell Publishing Ltd  (3)
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  • 1
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In Escherichia coli, a lacZ fusion to the gabT gene is activated by the accumulation of two self-produced extracellular signals, indole and a second unidentified signal (signal-2). Extracellular indole contributes approximately 25% of this activation and signal-2 is responsible for the majority of activation. Using an E. coli strain unable to produce indole and containing a gabT::lacZ fusion, a genetic approach was used to search for genes involved in the production of signal-2. A spontaneous E. coli mutant, MJ1, exhibited significantly less signal-2 activity based on the ability of spent culture supernatants from this mutant to activate the gabT::lacZ fusion. Genetic analysis of MJ1 revealed that it contained two mutations, one in thyA and a second unknown mutation, designated spl1 (signal production locus) that led to loss of signal-2 production. The spl1 second-site mutation arises at high frequency in a thyA− background because it suppresses the loss of viability. This study demonstrates that mutations in deoB and deoC were capable of suppressing the loss of viability in thyA mutants and concomitantly resulted in loss of signal-2 activity in conditioned medium. Interestingly, both deoB and deoC mutations in an otherwise wild-type background resulted in higher levels of gabT::lacZ expression in cells at low density. It is hypothesized that deoB and deoC mutations result in an enhanced rate of signal-2 uptake and thus deplete signal-2 from the external medium.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Using a mini-Tn5lacZ1 reporter transposon, lacZ fusions have been identified in Proteus mirabilis that are activated by the accumulation of self-produced extracellular signals. Genes identified by this approach include putative homologs of pgm, nlpA and two genes of unknown function. The extracellular signal(s) involved in activation were resistant to the effects of acid and alkali. The signal required for activation of (nlpA) cma482::lacZ was sensitive to protease, suggesting the signal is a peptide or small protein. The signals behaved as polar molecules and were not extractable with ethyl acetate. A mini-Tn5Cm insertion was identified in a probable ptsI homolog that blocked activation of the cma134::lacZ fusion by an extracellular signal. The ptsI mutation did not alter extracellular signal production and may have a role in signal response.
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  • 3
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The AarP protein in Providencia stuartii encodes a small transcriptional activator which activates the chromosomal aminoglycoside acetyltransferase aac(2′)-Ia gene. In addition, AarP activates genes involved in a multiple antibiotic resistance (Mar) phenotype. Expression of an aarP–lacZ fusion increased in a density-dependent manner and reached peak levels at stationary phase. The expression of an aarP–lacZ fusion could be prematurely activated in cells at early to mid-exponential phase by the addition of spent culture supernatants from stationary phase cultures or by ethyl acetate extracts of these supernatants. Nutrient starvation had a negligible effect on aarP expression. In a search for mutations that block aarP activation at stationary phase, a mini-Tn5Cm insertion has been identified within a gene whose product was 77% identical to SspA, a regulatory protein involved in stationary phase gene expression and virulence. An unmarked sspA null allele (sspA2) was created by allelic replacement to further examine the role of sspA in P. stuartii. The sspA2 allele resulted in substantial decrease in aarP mRNA accumulation at various phases of growth. Furthermore, in an sspA mutant background, the aarP–lacZ fusion was no longer activated by an extracellular signal.
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