專題：Nature報導
RNA聚合酶-II（Pol II）是在基因轉錄中起中心作用的酶，在真核細胞中製造所有的信使RNA。蛋白編碼基因的轉錄是由Pol II和包括TFIIB在內的一般性轉錄因子所形成的一個複合物啟動的。
Kostrewa等人確定了Pol II/TFIIB複合物的完整晶體結構。該結構及互補功能數據表明，轉錄的啟動有一個由6個步驟構成的機制，包括當轉錄開始點被定位後所觸發的向RNA伸長的過渡。（生物谷Bioon.com）
生物谷推薦原始出處：
Nature 462, 323-330 (19 November 2009) | doi:10.1038/nature08548
RNA polymerase II–TFIIB structure and mechanism of transcription initiationnear-final version
Dirk Kostrewa1,3, Mirijam E. Zeller2,3, Karim-Jean Armache1,3,4, Martin Seizl1, Kristin Leike1, Michael Thomm2 & Patrick Cramer1
1 Gene Center Munich and Center for Integrated Protein Science Munich (CIPSM), Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universit?t München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
2 Institut für Biochemie, Genetik und Mikrobiologie, Universit?t Regensburg, Universit?tsstrasse 31, 93053 Regensburg, Germany
3 These authors contributed equally to this work.
4 Present address: Department of Molecular Biology, Massachusetts General Hospital and Department of Genetics, Harvard Medical School, Boston, Massachusetts 02114, USA.
5 Correspondence to: Patrick Cramer1 Correspondence and requests for materials should be addressed to P.C.
To initiate gene transcription, RNA polymerase II (Pol II) requires the transcription factor IIB (B). Here we present the crystal structure of the complete Pol II–B complex at 4.3 ? resolution, and complementary functional data. The results indicate the mechanism of transcription initiation, including the transition to RNA elongation. Promoter DNA is positioned over the Pol II active centre cleft with the 'B-core' domain that binds the wall at the end of the cleft. DNA is then opened with the help of the 'B-linker' that binds the Pol II rudder and clamp coiled-coil at the edge of the cleft. The DNA template strand slips into the cleft and is scanned for the transcription start site with the help of the 'B-reader' that approaches the active site. Synthesis of the RNA chain and rewinding of upstream DNA displace the B-reader and B-linker, respectively, to trigger B release and elongation complex formation.