Structural Basis of RNA Polymerase I Transcription Initiation

Publication date: 23 March 2017
Source:Cell, Volume 169, Issue 1
Author(s): Christoph Engel, Tobias Gubbey, Simon Neyer, Sarah Sainsbury, Christiane Oberthuer, Carlo Baejen, Carrie Bernecky, Patrick Cramer
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.

Graphical abstract

Teaser

RNA polymerase I explores DNA deformability to recognize where to start transcribing.


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