title: Na+-induced transcription of nhaA, which encodes an Na+/H+ antiporter in Escherichia coli, is positively regulated by nhaR and affected by hns.
abstract: nhaA encodes an Na+/H+ antiporter in Escherichia coli which is essential for adaptation to high salinity and alkaline pH in the presence of Na+. We used Northern (RNA) analysis to measure directly the cellular levels of nhaA mRNA. NhaR belongs to the LysR family of regulatory proteins. Consistent with our previous data with an nhaA'-'lacZ fusion, NhaR was found to be a positive regulator and Na+ was found to be a specific inducer of nhaA transcription. In the nhaA'-'lacZ fusion, maximal induction was observed at alkaline pH. In contrast, in the nhaA+ strain both the level of nhaA expression and the induction ratio were lower at alkaline pH. This difference may be due to the activity of NhaA in the wild-type strain as NhaA efficiently excreted Na+ at alkaline pH and reduced the intracellular concentration of Na+, the signal for induction. We also showed that although the global regulator rpoS was not involved in nhaA regulation, the global regulator hns played a role. Thus, the expression of nhaA'-'lacZ was derepressed in strains bearing hns mutations and transformation with a low-copy-number plasmid carrying hns repressed expression and restored Na+ induction. The derepression in hns strains was nhaR independent. Most interestingly, multicopy nhaR, which in an hns+ background acted only as an Na+-dependent positive regulator, acted as a repressor in an hns strain in the absence of Na+ but was activated in the presence of the ion. Hence, an interplay between nhaR and hns in the regulation of nhaA was suggested.
authors.affiliation: Division of Microbial and Molecular Ecology, Institute of Life Sciences, Hebrew University of Jerusalem, Israel.
authors.forename: N
authors.initials: N
authors.lastname: Dover
authors.forename: C F
authors.initials: CF
authors.lastname: Higgins
authors.forename: O
authors.initials: O
authors.lastname: Carmel
authors.forename: A
authors.initials: A
authors.lastname: Rimon
authors.forename: E
authors.initials: E
authors.lastname: Pinner
authors.forename: E
authors.initials: E
authors.lastname: Padan
mesh_terms: D000220:Adaptation, Biological; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D001692:Biological Transport; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D029968:Escherichia coli Proteins; D018628:Gene Dosage; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D006863:Hydrogen-Ion Concentration; D012808:Sigma Factor / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D012808:Sigma Factor; D017923:Sodium-Hydrogen Exchangers; D014157:Transcription Factors; C074687:nhaR protein, E coli; C069567:sigma factor KatF protein, Bacteria; D012964:Sodium