Article abstract
Nature Structural & Molecular Biology 15, 811 - 818 (2008)
Published online: 13 June 2008 | doi:10.1038/nsmb.1458
Structural basis of transcription inhibition by 
-amanitin and implications for RNA polymerase II translocation
Florian Brueckner1 & Patrick Cramer1
Abstract
To study how RNA polymerase II translocates after nucleotide incorporation, we prepared elongation complex crystals in which pre- and post-translocation states interconvert. Crystal soaking with the inhibitor 
-amanitin locked the elongation complex in a new state, which was refined at 3.4-Å resolution and identified as a possible translocation intermediate. The DNA base entering the active site occupies a 'pretemplating' position above the central bridge helix, which is shifted and occludes the templating position. A leucine residue in the trigger loop forms a wedge at the shifted bridge helix, but moves by 13 Å to close the active site during nucleotide incorporation. Our results support a Brownian ratchet mechanism that involves swinging of the trigger loop between open, wedged and closed positions, and suggest that -amanitin impairs nucleotide incorporation and translocation by trapping the trigger loop and bridge helix.
- Gene Center and Center for Integrated Protein Science Munich (CIPSM), Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany.
Correspondence to: Patrick Cramer1 e-mail: cramer@LMB.uni-muenchen.de
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