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use of sigma 54 as transcription factor

What is a sigma factor?

  • prokaryotic transcription initiation factor
  • enables binding of RNA polymerase to gene promoter
  • activation dependent on different environmental conditions

In E.coli

  • sigma54
  • sigma70

sigma 54 versus sigma70

  • There is limited amino-acid similarity between sigma54 and sigma70.
  • sigma70
  1. sigma70-RNAP: positive and negative regulation
  2. transcribes most housekeeping genes
  3. RNAP–70 holoenzyme is competent for transcription
  • sigma54
  1. sigma54-RNAP: positive regulation
  2. controls transcription of genes expressed under specific environmental conditions
  3. RNAP–54 complex binds to promoter DNA, but remains stalled and unable to transcribe. When the activator protein PspF binds to a bacterial enhancer-like sequence in the promoter and hydrolyses ATP, the RNAP–54 complex is converted from a closed to an open complex that can actively transcribe. Activation of RNAP–54 transcription by PspF (activator protein) is analogous to activation of RNA polymerase II-mediated transcription in eukaryotes by the ATP-hydrolysing protein TFIIH.[[1]]
  4. less basal transcription which means less noise.[[2]]


  1. http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WSR-4TVSH9K-5-1&_cdi=7053&_user=217827&_pii=S1097276508006916&_orig=search&_coverDate=11%2F07%2F2008&_sk=999679996&view=c&wchp=dGLzVtz-zSkzk&md5=c52f52f0737fbd12b741713839e1aed8&ie=/sdarticle.pdf
  2. http://jb.asm.org/cgi/reprint/181/24/7558