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. Author manuscript; available in PMC: 2009 Apr 1.
Published in final edited form as: Curr Opin Genet Dev. 2008 Feb 20;18(2):130–136. doi: 10.1016/j.gde.2007.12.008

Figure 1. Steps in transcription initiation.

Figure 1

A. Steps in transcription initiation in eubacteria.
  1. Preinitiation closed complex formation at the promoter by RNAP holoenzyme (containing a σ factor).
  2. DNA is unwound around the transcription start site to form an open complex.
  3. Abortive synthesis of 2–15 nt RNAs requiring DNA “scrunching”.
  4. Promoter escape is typically associated with loss of σ factor.
B. Steps in transcription initiation in eukaryotes.
  1. Preinitiation complex formation at the promoter with Pol II and general transcription factors.
  2. DNA is unwound around the transcription start site to form an open complex.
  3. Abortive synthesis of 2–3 nt RNAs.
  4. Promoter escape is associated with release of most general transcription factors and with phosphorylation at Serine 5 of the C-terminal domain of the largest Pol II subunit (red circle). In some eukaryotes Pol II pauses after synthesis of 20–50 nt RNAs.
  5. Escape from promoter-proximal pauses is associated with phosphorylation at Serine 2 of the C-terminal domain of the largest Pol II subunit (green circle) by pTEFb.