Nitrate repression of the Escherichia coli pfl operon is mediated by the dual sensors NarQ and NarX and the dual regulators NarL and NarP.
AUTOR(ES)
Kaiser, M
RESUMO
The pfl operon is expressed at high levels anaerobically. Growth of Escherichia coli in the presence of nitrate or nitrite led to a 45% decrease in expression when cells were cultivated in rich medium. Nitrate repression, however, was significantly enhanced (sevenfold) when the cells were cultured in minimal medium. Regulation of pfl expression by nitrate was dependent on the NarL, NarP, NarQ, and NarX proteins but independent of FNR, ArcA, and integration host factor, which are additional regulators of pfl expression. Strains unable to synthesize any one of the NarL, NarP, NarQ, or NarX proteins, but retaining the capacity to synthesize the remaining three, exhibited essentially normal nitrate regulation. In contrast, narL narP and narX narQ double null mutants were devoid of nitrate regulation when cultured in rich medium but they retained some nitrate repression (1.3-fold) when grown in minimal medium. By using lacZ fusions, it was possible to localize the DNA sequences required to mediate nitrate repression to the pfl promoter-regulatory region. DNase I footprinting studies identified five potential binding sites for the wild-type NarL protein in the pfl promoter-regulatory region. Specific footprints were obtained only when NarL was phosphorylated with acetyl phosphate before the binding reaction was performed. Each of the protected regions contained at least one heptamer sequence which has been deduced from mutagenesis studies to be essential for NarL binding (K. Tyson, A. Bell, J. Cole, and S. Busby, Mol. Microbiol. 7:151-157, 1993).
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=177079Documentos Relacionados
- Dual response regulators (NarL and NarP) interact with dual sensors (NarX and NarQ) to control nitrate- and nitrite-regulated gene expression in Escherichia coli K-12.
- Expression of the narX, narL, narP, and narQ genes of Escherichia coli K-12: regulation of the regulators.
- The NarX and NarQ sensor-transmitter proteins of Escherichia coli each require two conserved histidines for nitrate-dependent signal transduction to NarL.
- Phosphorylation and dephosphorylation of the NarQ, NarX, and NarL proteins of the nitrate-dependent two-component regulatory system of Escherichia coli.
- Structure of genes narL and narX of the nar (nitrate reductase) locus in Escherichia coli K-12.