Disease relevance of narX

• The narX and narL genes encoding the nitrate-sensing regulators of Escherichia coli are homologous to a family of prokaryotic two-component regulatory genes [1].

High impact information on narX

• The narX, narQ and narL genes of Escherichia coli encode a nitrate-responsive two-component regulatory system that controls the expression of many anaerobic electron-transport- and fermentation-related genes [2].
• In this study we report the isolation and characterization of narX* (star) mutants that constitutively activate nitrate reductase (narGHJI) gene expression and repress fumarate reductase (frdABCD) gene expression when no nitrate is provided for the cell [2].
• The narQ gene was cloned, sequenced, and compared with the narX gene [3].
• The narL and narX gene products are required for this nitrate-dependent control, and apparently function as members of a two-component regulatory system [3].
• 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 [3].

Biological context of narX

• First, narL null mutants retain residual nitrate induction of fdnG operon expression; this residual induction is absent in narX narQ double-null strains [4].
• We report here the nucleotide sequences of narL and narX [5].
• In the screening, it was suggested that two mRNAs from the histidine kinase genes, narX and yojN, in a two-component signal transduction system, were extremely unstable [6].
• We observed that insertions in narX (also of unknown function) significantly relieved nitrate inhibition of fumarate reductase gene expression [7].
• Multicopy plasmids containing both narL+ and narX+ or only narL+ were able to complement narL mutants, whereas narX+ plasmids complemented narX mutants only when present in a copy number approximately equal to that of narL [8].

Associations of narX with chemical compounds

• These data establish a clear role for the narX gene product in gene regulation and strongly suggest its role in sensing nitrate and molybdenum [9].
• This regulation requires molybdate and is mediated by the narX and narL gene products, which together form a two-component regulatory system [9].
• We have previously identified a locus called frdR which pleiotropically affects nitrate repression of fumarate reductase, trimethylamine N-oxide reductase, and alcohol dehydrogenase gene expression and nitrate induction of nitrate reductase expression (L. V. Kalman and R. P. Gunsalus, J. Bacteriol. 170:623-629, 1988) [8].
• The frdR mutant was also derepressed for nitrate control of the trimethylamine-N-oxide reductase and alcohol dehydrogenase enzymes [10].

Other interactions of narX

• narL and narX mediate nitrate induction of nitrate reductase synthesis and nitrate repression of fumarate reductase synthesis [5].
• Analysis of these operon fusions indicated that narL and narX are transcribed counterclockwise with respect to the E. coli genetic map and that narK is transcribed clockwise [11].
• Expression of phi (narX-lacZ) operon fusions was induced by nitrate and was decreased by narL and fnr mutations [11].
• DNA truncation experiments for fnr and narX genes indicated that multiple anaero-boxes in each promoter region are essential for repression by the FNR protein, but they also suggest that factor-independent upstream activation signals are operating with these promoters [12].
• These narX* alleles also caused the induction of nitrate reductase gene expression and the repression of a dmsA-lacZ fusion in the absence of nitrate [9].

References