Disease relevance of ECs1726

• Nitrate acts through the response regulator NarL to activate and repress anaerobic respiratory gene expression in Escherichia coli [1].
• Genetic evidence that NarL function is not required for nitrate regulation of nitrate assimilation in Klebsiella pneumoniae M5al [2].
• The Pseudomonas aeruginosa hemA promoter is regulated by Anr, Dnr, NarL and Integration Host Factor [3].

High impact information on ECs1726

• Dimerization allows DNA target site recognition by the NarL response regulator [4].
• However, previous work discovered that NarL-mediated nitrate regulation is essentially normal in delta narX deletion mutants [1].
• Previous work has identified two cis-acting sites in the nar operon control region: a proximal site required for anaerobic induction mediated by the activator Fnr and a remote upstream site required for nitrate induction mediated by the activator NarL [Li, S. & DeMoss, J. A. (1988) J. Biol. Chem. 263, 13700-13705] [5].
• The C-terminal domain is composed of four alpha-helices where two central helices form a helix-turn-helix motif similar to the structures of the regulatory proteins GerE, NarL, and TraR [6].
• Both the phosphorylation and dephosphorylation of NarL required Mg2+, and neither reaction was affected by the presence of nitrate [7].

Chemical compound and disease context of ECs1726

• Expression from the Escherichia coli nir promoter is co-dependent on Fnr (a transcription factor triggered by oxygen starvation) and on NarL or NarP (transcription factors triggered by nitrite and nitrate ions) [8].
• Hierarchical control of anaerobic gene expression in Escherichia coli K-12: the nitrate-responsive NarX-NarL regulatory system represses synthesis of the fumarate-responsive DcuS-DcuR regulatory system [9].
• The Escherichia coli K-12 NarL and NarP Proteins Insulate the nrf Promoter from the Effects of Integration Host Factor [10].

Biological context of ECs1726

• A base sequence no longer than 27 bp, located at about -200 bp, was essential for the stimulation by nitrate coupled with NarL [11].
• Integration host factor protein (IHF) was shown to be required for Fnr- and NarL-dependent activation of the nitrate reductase (narGHJI) operon of Escherichia coli in response to nitrate availability and anaerobiosis [12].
• Further stimulation of transcription occurs in the presence of nitrate and is dependent on activation of the transacting factor NarL and a cis-acting sequence (NarL box) located approximately 200 base pairs upstream from the transcription start site [13].
• To define the structure of the NarL box, alterations in the NarL box region, generated by saturation mutagenesis of the sequence from positions -184 to -202 in the narGHJI promoter of a narG::lacZ fusion-bearing plasmid, were analyzed for their effects on NarL-mediated stimulation of transcription [13].
• Furthermore, shifting of most of the intervening sequence or defined segments of the sequence by 4 bases while maintaining the position of the NarL box relative to sequences required for Fnr-dependent, anaerobic transcription also eliminated the NarL-mediated stimulation [13].

Associations of ECs1726 with chemical compounds

• The relative stabilities of the phosphorylated forms of the two proteins at different pH values were consistent with the proposal that, in analogy to other related two-component regulatory systems, NarX and NarL were phosphorylated on specific histidine and aspartate residues, respectively [7].
• NarL-phosphate, stabilized by the addition of EDTA, ran as a monomer on gel filtration [7].
• These mutations also suppress induction by nitrite: single mutations at symmetry-related positions have similar effects, whilst double mutations have more severe effects, probably because two NarL subunits bind to the inverted repeat [14].
• By gel retardation and DNase I protection studies, we have demonstrated that NarL-phosphate, produced by the reaction of purified NarL with acetyl phosphate, specifically binds to a fragment derived from the upstream region of the narG promoter [15].
• Therefore, expression of nuo is regulated by O2 and nitrate via ArcA, NarL, FNR and IHF at sites within the -277 region, and by other factors including C4 dicarboxylates at a site between -277 and -899 [16].

Analytical, diagnostic and therapeutic context of ECs1726

• This was accomplished by introducing single cysteine amino acid replacements at selected locations within the carboxy-terminal DNA-binding domain in or nearby the helix 8 to helix 9 region of the NarL protein using site-directed mutagenesis [17].
• Gel retardation assays were used to show that FNR (fumarate-nitrate regulation) and NarL form a complex with the hcp promoter [18].
• Microarray analysis of gene regulation by oxygen, nitrate, nitrite, FNR, NarL and NarP during anaerobic growth of Escherichia coli: new insights into microbial physiology [19].

References