Modular structure of FixJ: homology of the transcriptional activator domain with the -35 binding domain of sigma factors

Mol Microbiol. 1991 Apr;5(4):987-97. doi: 10.1111/j.1365-2958.1991.tb00774.x.


The FixL/FixJ two-component system is a global regulator of nitrogen-fixation genes in Rhizobium meliloti. The transcriptional activator FixJ contains two modules: its N-terminal module is homologous with other two-component regulators; its C-terminal module shows homology with various transcriptional activators, and with the C-terminal region of sigma factors, which is involved in the discrimination of the -35 region of bacterial promoters. We show that the C-terminal module of FixJ contains the entire transcription activation function, and that the N-terminal module regulates this activity negatively. Oligonucleotide-directed mutagenesis of the transcriptional activator module demonstrated the importance of a potential helix-turn-helix structure.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • DNA Mutational Analysis
  • Genes, Bacterial*
  • Macromolecular Substances
  • Molecular Sequence Data
  • Nitrogen Fixation / genetics*
  • Plasmids / genetics
  • Promoter Regions, Genetic
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism
  • Rhizobium / genetics*
  • Sequence Homology, Nucleic Acid
  • Sigma Factor / genetics*
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism


  • Bacterial Proteins
  • Macromolecular Substances
  • Repressor Proteins
  • Sigma Factor
  • Transcription Factors
  • FixJ protein, Bacteria