The function of isolated domains and chimaeric proteins constructed from the transcriptional activators NifA and NtrC of Klebsiella pneumoniae

Mol Microbiol. 1990 Jan;4(1):29-37. doi: 10.1111/j.1365-2958.1990.tb02012.x.


A model for the domain structure of sigma 54-dependent transcriptional activators, based on sequence data, has been tested by examining the function of truncated and chimaeric proteins. Removal of the N-terminal domain of NtrC abolishes transcriptional activation, indicating that this domain is positively required for activator function. Over-expression of this domain as a separate peptide appears to titrate out the phosphorylating activity of NtrB. Removal of the N-terminal domain of NifA reduces activation 3-4-fold. The residual activity is particularly sensitive to inhibition by NifL, suggesting that the role of the N-terminal domain is to block the action of NifL in derepressing conditions. The C-terminal domain of NtrC showed repressor activity when expressed as a separate peptide. This domain is necessary for activator function even when NtrC binding sites are deleted from promoters. A point mutation in the ATP-binding motif of the NtrC central domain, Ser169 to Ala, also abolished activator function. Exchanging the N-terminal domains of Klebsiella pneumoniae NtrC, NifA and Escherichia coli OmpR, did not produce any hybrid activity, suggesting that N-terminal domains in the native proteins specifically recognize the rest of the molecule.

MeSH terms

  • Bacterial Proteins / genetics*
  • Base Sequence
  • DNA-Binding Proteins / genetics*
  • Escherichia coli Proteins
  • Gene Expression Regulation, Bacterial
  • Klebsiella pneumoniae / genetics*
  • Molecular Sequence Data
  • Mutation
  • PII Nitrogen Regulatory Proteins
  • Recombinant Fusion Proteins
  • Trans-Activators*
  • Transcription Factors / genetics*


  • Bacterial Proteins
  • DNA-Binding Proteins
  • Escherichia coli Proteins
  • NifA protein, Bacteria
  • PII Nitrogen Regulatory Proteins
  • Recombinant Fusion Proteins
  • Trans-Activators
  • Transcription Factors
  • glnG protein, E coli