A conserved region in the sigma54-dependent activator DctD is involved in both binding to RNA polymerase and coupling ATP hydrolysis to activation

Mol Microbiol. 1997 Oct;26(2):373-86. doi: 10.1046/j.1365-2958.1997.5851955.x.


Rhizobium melioti DctD activates transcription from the dctA promoter by catalysing the isomerization of closed complexes between sigma54-RNA polymerase holoenzyme and the promoter to open complexes. DctD must make productive contact with sigma54-holoenzyme and hydrolyse ATP to catalyse this isomerization. To define further the activation process, we sought to isolate mutants of DctD that had reduced affinities for sigma54-holoenzyme. Mutagenesis was confined to the well-conserved C3 region of the protein, which is required for coupling ATP hydrolysis to open complex formation in sigma54-dependent activators. Mutant forms of DctD that failed to activate transcription and had substitutions in the C-terminal half of the C3 region were efficiently cross-linked to sigma54 and the beta-subunit of RNA polymerase, suggesting that they bound normally to sigma54-holoenzyme. In contrast, some mutant forms of DctD with amino acid substitutions in the N-terminal half of the C3 region had reduced affinities for sigma54 and the beta-subunit in the cross-linking assay. These data suggest that the N-terminal half of the C3 region of DctD contains a site that may contact sigma54-holoenzyme during open complex formation.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Binding Sites
  • Conserved Sequence
  • DNA-Directed RNA Polymerases / genetics
  • DNA-Directed RNA Polymerases / metabolism*
  • Dimaprit / analogs & derivatives*
  • Dimaprit / metabolism
  • Gene Expression Regulation, Bacterial
  • Hydrolysis
  • Molecular Sequence Data
  • Mutation
  • Sequence Alignment
  • Sinorhizobium meliloti / genetics
  • Sinorhizobium meliloti / metabolism*
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism


  • Bacterial Proteins
  • Transcription Factors
  • dctD protein, Rhizobium meliloti
  • APT
  • DNA-Directed RNA Polymerases
  • Dimaprit