Department of Cell Biology, The Scripps Research Institute, La Jolla, California, USA.
Nat Struct Mol Biol. 2010 Mar;17(3):273-9. doi: 10.1038/nsmb.1757. Epub 2010 Feb 14.
We used single-particle electron microscopy to characterize the structure and subunit organization of the Mediator Head module that controls Mediator-RNA polymerase II (RNAPII) and Mediator-promoter interactions. The Head module adopts several conformations differing in the position of a movable jaw formed by the Med18-Med20 subcomplex. We also characterized, by structural, biochemical and genetic means, the interactions of the Head module with TATA-binding protein (TBP) and RNAPII subunits Rpb4 and Rpb7. TBP binds near the Med18-Med20 attachment point and stabilizes an open conformation of the Head module. Rpb4 and Rpb7 bind between the Head jaws, establishing contacts essential for yeast-cell viability. These results, and consideration of the structure of the Mediator-RNAPII holoenzyme, shed light on the stabilization of the pre-initiation complex by Mediator and suggest how Mediator might influence initiation by modulating polymerase conformation and interaction with promoter DNA.
我们使用单颗粒电子显微镜来描绘控制 Mediator-RNA 聚合酶 II（RNAPII）和 Mediator-启动子相互作用的 Mediator 头部模块的结构和亚基组织。头部模块采用了几种构象，这些构象在由 Med18-Med20 亚基组成的可移动下颚的位置上有所不同。我们还通过结构、生化和遗传手段，研究了头部模块与 TATA 结合蛋白（TBP）和 RNAPII 亚基 Rpb4 和 Rpb7 的相互作用。TBP 结合在 Med18-Med20 附着点附近，并稳定头部模块的开放构象。Rpb4 和 Rpb7 结合在头部下颚之间，建立了对酵母细胞活力至关重要的接触。这些结果，以及对 Mediator-RNAPII 全酶结构的考虑，阐明了 Mediator 对起始前复合物的稳定作用，并提出了 Mediator 如何通过调节聚合酶构象和与启动子 DNA 的相互作用来影响起始的机制。
