Structural Basis of RNA Polymerase I Transcription Initiation

Cell. 2017 Mar 23;169(1):120-131.e22. doi: 10.1016/j.cell.2017.03.003.


Transcription initiation at the ribosomal RNA promoter requires RNA polymerase (Pol) I and the initiation factors Rrn3 and core factor (CF). Here, we combine X-ray crystallography and cryo-electron microscopy (cryo-EM) to obtain a molecular model for basal Pol I initiation. The three-subunit CF binds upstream promoter DNA, docks to the Pol I-Rrn3 complex, and loads DNA into the expanded active center cleft of the polymerase. DNA unwinding between the Pol I protrusion and clamp domains enables cleft contraction, resulting in an active Pol I conformation and RNA synthesis. Comparison with the Pol II system suggests that promoter specificity relies on a distinct "bendability" and "meltability" of the promoter sequence that enables contacts between initiation factors, DNA, and polymerase.

Keywords: RNA polymerase I; X-ray crystallography; core factor; cryo-EM; ribosomal RNA promoter; transcription initiation.

MeSH terms

  • Cryoelectron Microscopy
  • Crystallography, X-Ray
  • Models, Molecular
  • Multiprotein Complexes / chemistry
  • Multiprotein Complexes / metabolism
  • Multiprotein Complexes / ultrastructure
  • Promoter Regions, Genetic
  • RNA Polymerase I / chemistry
  • Saccharomyces cerevisiae / chemistry*
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae / ultrastructure
  • Saccharomyces cerevisiae Proteins / chemistry*
  • Saccharomyces cerevisiae Proteins / metabolism
  • Saccharomyces cerevisiae Proteins / ultrastructure
  • Transcription Initiation, Genetic*
  • Transcription, Genetic


  • Multiprotein Complexes
  • Saccharomyces cerevisiae Proteins
  • RNA Polymerase I