Journal
MOLECULAR MICROBIOLOGY
Volume 50, Issue 4, Pages 1391-1399Publisher
BLACKWELL PUBLISHING LTD
DOI: 10.1046/j.1365-2958.2003.03776.x
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- NIGMS NIH HHS [GM36877] Funding Source: Medline
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Respiratory enzyme synthesis in enterobacteria is controlled in response to electron acceptor availability. The iron-sulphur protein Fnr and the sensor-regulator proteins ArcB-ArcA control respiratory gene transcription in response to oxygen and quinone pool redox status respectively. The sensor-regulator proteins NarX-NarL and NarQ-NarP control anaerobic respiratory gene expression in response to nitrate and nitrite. Our laboratory recently engineered the lac operon to replace the primary operator O1-lac with the NarL and NarP protein binding site from the nirB operon. Expression of the lacZ gene from this construct is repressed by nitrate in Nar(+) strains. Here, we found that lacZ gene expression was repressed in aerated cultures of narQ(+)narX null strains. This repression was not observed in narX(+)narQ(+) or narX(+)narQ null strains. Thus, the NarQ sensor responds to aeration as well as to nitrate and nitrite. The NarX and NarQ sensors are composed of three distinct modules: an amino-terminal sensory module, a carboxyl-terminal transmitter module and a central module of unknown function. Experiments with NarX-NarQ hybrid proteins suggest that the NarQ protein central module is necessary for response to aeration. The physiological significance of this additional sensory role for the NarQ sensor remains obscure.
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