title: Studies on the roles of GlnK and GlnB in regulating Klebsiella pneumoniae NifL-dependent nitrogen control.
abstract: In Klebsiella pneumoniae, nitrogen fixation (nif) genes are regulated in response to fixed nitrogen and oxygen. The activity of the nif-specific transcriptional activator NifA is modulated by NifL, which mediates both oxygen and nitrogen control. The signal transduction protein GlnK is required to relieve the inhibitory effect of NifL on NifA that occurs when the intracellular N status is high and in a wild-type cell, the action of GlnK cannot be substituted by the structurally related protein PII. We have studied the modulation of NifA activity by NifL in an heterologous system in which the host organism is Escherichia coli. Using a DeltaglnB, DeltaglnK mutant, we have shown that the modulation of NifA activity by NifL is dependent on the concentration of GlnK in the cell and that when overproduced, PII can substitute for GlnK. Furthermore, our data suggest that PII can counteract the positive action of GlnK in relieving NifL-dependent inhibition of NifA activity. This negative effect of PII may be physiologically important in establishing repression of nif gene expression when the intracellular nitrogen status rises.
authors.affiliation: Department of Molecular Microbiology, John Innes Centre, Norwich, UK.
authors.forename: T
authors.initials: T
authors.lastname: Arcondéguy
authors.forename: W C
authors.initials: WC
authors.lastname: van Heeswijk
authors.forename: M
authors.initials: M
authors.lastname: Merrick
mesh_terms: D001426:Bacterial Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007711:Klebsiella pneumoniae / Q000235:genetics / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000235:genetics; D051922:PII Nitrogen Regulatory Proteins; D014157:Transcription Factors / Q000187:drug effects / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C113488:GlnK protein, Azorhizobium caulinodans; C061338:NifA protein, Bacteria; D051922:PII Nitrogen Regulatory Proteins; D014157:Transcription Factors; C084296:nifL protein, Bacteria; C404143:PIID regulatory protein, Bacteria; D009584:Nitrogen