The Rhodobacter sphaeroides ECF sigma factor, sigma(E), and the target promoters cycA P3 and rpoE P1

J Mol Biol. 1999 Nov 26;294(2):307-20. doi: 10.1006/jmbi.1999.3263.


Rhodobacter sphaeroides rpoE encodes a 19.2 kDa protein, sigma(E), related to members of the extra-cytoplasmic function subfamily of eubacterial RNA polymerase sigma factors. We demonstrate that sigma(E) directs transcription from rpoE P1, the promoter for the rpoEchrR operon, and from cycA P3, a promoter for the cytochrome c2 structural gene. Comparison of these sigma(E)-dependent promoters reveals significant sequence conservation in their -35 and -10 regions; however, rpoE P1 is over 80-fold stronger than cycA P3. Both promoters contain identical -35 hexamers, (-36)TGATCC(-31), that appear to constitute the preferred sequence, since any single base mutation in this region of cycA P3 reduces promoter function. The higher activity of rpoE P1 appears to reflect a better -10 region, (-13)TAAGA(-9), as it contains four out of five of the nucleotides found to be important to sigma(E)-dependent transcription. We also propose that ChrR acts as an inhibitor of sigma(E), since these two proteins can form a complex, and DeltachrR mutations increase sigma(E)-dependent transcription. ChrR is believed to respond to a signal from tetrapyrrole biosynthesis because loss of function mutations in chrR lead to cohemin resistance. Based on our observations, we present a model in which cohemin resistance is conferred by increasing sigma(E) activity.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / drug effects
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Cytochrome c Group / genetics*
  • Cytoplasm / genetics
  • Cytoplasm / metabolism
  • DNA Mutational Analysis
  • Drug Resistance, Microbial / genetics
  • Gene Expression Regulation, Bacterial
  • Heme / pharmacology
  • Hemin
  • Histidine / genetics
  • Molecular Sequence Data
  • Point Mutation
  • Promoter Regions, Genetic*
  • Regulatory Sequences, Nucleic Acid
  • Rhodobacter sphaeroides / drug effects
  • Rhodobacter sphaeroides / genetics*
  • Sigma Factor / drug effects
  • Sigma Factor / genetics*
  • Sigma Factor / metabolism
  • Transcription Factors / drug effects
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism
  • Transcription, Genetic


  • Bacterial Proteins
  • ChrR protein, Rhodobacter sphaeroides
  • Cytochrome c Group
  • Sigma Factor
  • Transcription Factors
  • sporulation-specific sigma factors
  • Heme
  • Histidine
  • Hemin
  • cytochrome c(3)