Cheetham G M, Steitz T A
Department of Molecular Biophysics and Biochemistry, Yale University, Howard Hughes Medical Institute, New Haven, CT 06520-8114, USA.
Science. 1999 Dec 17;286(5448):2305-9. doi: 10.1126/science.286.5448.2305.
The structure of a T7 RNA polymerase (T7 RNAP) initiation complex captured transcribing a trinucleotide of RNA from a 17-base pair promoter DNA containing a 5-nucleotide single-strand template extension was determined at a resolution of 2.4 angstroms. Binding of the upstream duplex portion of the promoter occurs in the same manner as that in the open promoter complex, but the single-stranded template is repositioned to place the +4 base at the catalytic active site. Thus, synthesis of RNA in the initiation phase leads to accumulation or "scrunching" of the template in the enclosed active site pocket of T7 RNAP. Only three base pairs of heteroduplex are formed before the RNA peels off the template.
通过2.4埃的分辨率确定了T7 RNA聚合酶（T7 RNAP）起始复合物的结构，该复合物从含有5个核苷酸单链模板延伸的17个碱基对启动子DNA转录三核苷酸RNA。启动子上游双链部分的结合方式与开放启动子复合物中的结合方式相同，但单链模板被重新定位，使+4碱基位于催化活性位点。因此，起始阶段的RNA合成导致模板在T7 RNAP封闭的活性位点口袋中积累或“压缩”。在RNA从模板上剥离之前，仅形成三个碱基对的异源双链体。
