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Nitrogen is an essential nutrient for growth and is readily available to microbes in many environments in the form of ammonium and nitrate. Both ions are of environmental significance due to sustained use of inorganic fertilizers on agricultural soils. Diverse species of bacteria that have an assimilatory nitrate/nitrite reductase system (NAS) can use nitrate or nitrite as the sole nitrogen source for growth when ammonium is limited. In Paracoccus denitrificans, the pathway-specific two-component regulator for NAS expression is encoded by the nasT and nasS genes. Here, we show that the putative RNA-binding protein NasT is a positive regulator essential for expression of the nas gene cluster (i.e. nasABGHC). By contrast, a nitrogen oxyanion-binding sensor (NasS) is required for nitrate/nitrite-responsive control of nas gene expression. The NasS and NasT proteins co-purify as a stable heterotetrameric regulatory complex, NasS-NasT. This protein-protein interaction is sensitive to nitrate and nitrite, which cause dissociation of the NasS-NasT complex into monomeric NasS and an oligomeric form of NasT. NasT has been shown to bind the leader RNA for nasA. Thus, upon liberation from the complex, the positive regulator NasT is free to up-regulate nas gene expression.

Original publication




Journal article


J Biol Chem

Publication Date





29692 - 29702


Bacterial Metabolism, Bacterial Signal Transduction, Ligand-binding Protein, Nitrate Assimilation, Nitrogen Metabolism, Protein-Protein Interactions, RNA Signaling, Two-component Regulator, Anions, Bacteria, Bacterial Proteins, Electrophoresis, Polyacrylamide Gel, Gene Expression Regulation, Bacterial, Kinetics, Multigene Family, Mutation, Nitrates, Nitrite Reductase (NAD(P)H), Nitrites, Nitrogen, Oxygen, Paracoccus denitrificans, Protein Binding, Protein Multimerization, RNA, Bacterial, Signal Transduction, Spectrometry, Fluorescence