Identification and characterization of narQ, a second nitrate sensor for nitrate‐dependent gene regulation in Escherichia coli

Abstract

In response to nitrate availability, Escherichia coli regulates the synthesis of a number of enzymes involved in anaerobic respiration and fermentation. When nitrate is present, nitrate reductase (narGHJI) gene expression is induced, while expression of the DMSO/TMAO reductase (dmsABC), fumarate reductase (frdABCD) and fermentation related genes are repressed. The narL and narX gene products are required for this nitrate-dependent control, and apparently function as members of a two-component regulatory system. NarX is a presumed sensor-transmitter for nitrate and possibly molybdenum detection. The presumed response-regulator, NarL, when activated by NarX then binds at the regulatory DNA sites of genes to modulate their expression. In this study a third nitrate regulatory gene, narQ, was identified that also participates in nitrate-dependent gene regulation. Strains defective in either narQ or narX alone exhibited no nitrate-dependent phenotype whereas mutants defective in both narQ and narX were fully inactive for nitrate-dependent repression or activation. In all conditions tested, this regulation required a functional narL gene product. These findings suggest that the narX and narQ products have complementary sensor-transmitter functions for nitrate detection, and can work independently to activate NarL, for eliciting nitrate-dependent regulation of anaerobic electron transport and fermentation functions. The narQ gene was cloned, sequenced, and compared with the narX gene. Both gene products are similar in size, hydrophobicity, and sequence, and contain a highly conserved histidine residue common to sensor-transmitter proteins.

Enhanced metabolic versatility of planktonic sulfur-oxidizing γ-proteobacteria in an oxygen-deficient coastal ecosystem

“…The narK2KGHJI operon recovered from the metagenomic data ( Figure S18A) was associated and shares synteny with the operon described for the SUP05 metagenome from SI (Walsh et al, 2009), but that was absent from the GB metagenomes (Figure 2). In a different contig, we identified a two-component regulatory system nitrate/nitrite response regulator, related to NarX/L and a signal transduction histidine kinase nitrate/nitrite-specific, related to NarQ ( Figure S18B and Table S29); both genes have been shown to be associated with the regulation of the narGHIJ operon expression in Pseudomonas stutzeri and E. coli (Chiang et al, 1992;Dong et al, 1992;Walker and DeMoss, 1994). The narX/L gene is annotated as encoding a hypothetical protein, Sup05_1368, in the metagenome of the uncultured SI SUP05 (Walsh et al, 2009).…”

Control of electron flow in Escherichia coli: coordinated transcription of respiratory pathway genes

“…As a result, the existence of another regulator gene was proposed and was named narQ. narQ mutants that are defective in nitrate repression of frdA-lacZ expression were subsequently isolated (4). Analysis of these mutants reveals that NarQ and NarX can independently sense and respond to nitrate availability, although each requires NarL to effect nitrate-dependent transcription (4).…”

Signal transduction via the histidyl‐aspartyl phosphorelay

“…In contrast to the cascade of protein phosphorylation and dephosphorylation events in eukaryotes using protein tyrosine or serine/threonine kinases and phosphatases, the His-Asp phosphorelay systems in bacteria efficiently and reversibly regulate gene expression or cellular locomotion. The multiple steps in eukaryotes may have evolved to impart LA Egger et al 168 Genes to Cells (1997) In the centre column, the following pairs of E. coli sensor histidine kinases and responseregulators are shown: EnvZ/OmpR (Comeau et al 1985); CpxA/CpxR (Albin et al 1986;Dong et al 1993); PhoR/PhoB (Makino et al 1986a); PhoQ/PhoP (Kasahara et al 1992); BaeS/BaeR (Nagasawa et al 1993), NarX/NarL (Egan & Stewart 1990); NarQ/NarL (Chiang et al 1992); BasS/BasR (Nagasawa et al 1993), CreC/CreB (Amemura et al 1986), KdpD/KdpE (Walderhaug et al 1992); UhpB/UhpA (Friedrich & Kadner 1987;Weston & Kadner 1988); HydH/HydG (Blattner et al 1993); NtrB/NtrC (Miranda-Rios et al 1987); EvgS/EvgA (Utsumi et al 1994); RcsS/ RcsB (Stout et al 1990); ArcB/ArcA (Drury et al 1985); BarA (Nagasawa et al 1992;Zhang & Normark 1996); and CheA/CheY (Matsumura et al 1977(Matsumura et al , 1984. The sensor histidine kinase has a conserved C-terminal kinase domain of 240 amino acids (red rectangle) which contains: the histidine residue (H) that is autophosphorylated, an asparagine, DXGXG motif, a phenylalanine, and a GXGXG motif.…”