Concerted inhibition of the transcriptional activation functions of the enhancer-binding protein NIFA by the anti-activator NIFL

Mol Microbiol. 2001 Jan;39(2):480-93. doi: 10.1046/j.1365-2958.2001.02243.x.


The Azotobacter vinelandii NIFL regulatory flavoprotein responds to the redox, energy and nitrogen status of the cell to inhibit transcriptional activation by the sigmaN-dependent enhancer binding protein, NIFA, via the formation of a NIFL-NIFA protein complex. The NIFA protein contains three domains: an N-terminal domain of unknown function; a central catalytic domain required to couple nucleotide hydrolysis to activation of the sigmaN-RNA polymerase holoenzyme; and a C-terminal DNA-binding domain. We report that truncated NIFA proteins that either lack the amino-terminal domain or contain only the isolated central domain remain responsive to inhibition by NIFL but, in contrast to native NIFA, continue to hydrolyse nucleotides when NIFL is present. We also report that NIFL is competent to inhibit the DNA-binding function of NIFA. Taken together, these results suggest that NIFL inhibits NIFA via a concerted mechanism in which DNA binding, catalytic activity and, potentially, interaction with the polymerase are controlled by NIFL in order to prevent transcriptional activation under detrimental environmental conditions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Azotobacter vinelandii / genetics
  • Azotobacter vinelandii / metabolism*
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / drug effects*
  • Bacterial Proteins / metabolism
  • Bacterial Proteins / pharmacology*
  • DNA Footprinting
  • DNA, Bacterial / metabolism
  • DNA-Binding Proteins*
  • DNA-Directed RNA Polymerases / metabolism
  • Deoxyribonucleases / metabolism
  • Electrophoresis / methods
  • Gene Expression Regulation, Bacterial*
  • Nucleotides / metabolism
  • Phosphorylation
  • Plasmids / genetics
  • RNA Polymerase Sigma 54
  • Sigma Factor / metabolism
  • Transcription Factors / chemistry
  • Transcription Factors / drug effects*
  • Transcription Factors / metabolism
  • Transcriptional Activation / drug effects*


  • Bacterial Proteins
  • DNA, Bacterial
  • DNA-Binding Proteins
  • NifA protein, Bacteria
  • Nucleotides
  • Sigma Factor
  • Transcription Factors
  • nifL protein, Bacteria
  • DNA-Directed RNA Polymerases
  • RNA Polymerase Sigma 54
  • Deoxyribonucleases