Eukaryotic gene transcription requires the assembly at the promoter of a large preinitiation complex (PIC) that includes RNA polymerase II (Pol II) and the general transcription factors TFIID, TFIIA, TFIIB, TFIIF, TFIIE, and TFIIH. The size and complexity of Pol II, TFIID, and T FIIH have precluded their reconstitution from heterologous systems, and purification relies on scarce endogenous sources. Together with their conformational flexibility and the transient nature of their interactions, these limitations had precluded structural characterization of the PIC. In the last few years, however, progress in cryo-electron microscopy (cryo-EM) has made possible the visualization, at increasingly better resolution, of large PIC assemblies in different functional states. These structures can now be interpreted in near-atomic detail and provide an exciting structural framework for past and future functional studies, giving us unique mechanistic insight into the complex process of transcription initiation.
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机译：真核基因转录需要在大型预启动复合物（PIC）的启动子处组装，该复合物包括RNA聚合酶II（Pol II）和一般转录因子TFIID，TFIIA，TFIIB，TFIIF，TFIIE和TFIIH。 Pol II，TFIID和T FIIH的大小和复杂性使得它们无法从异源系统中重建，并且纯化依赖于稀有的内源性来源。这些限制以及它们的构象灵活性和交互作用的瞬态性质，使这些限制排除了PIC的结构表征。然而，在过去的几年中，低温电子显微镜（cryo-EM）的进步使得在不同功能状态下大型PIC组件的可视化（分辨率越来越高）成为可能。这些结构现在可以以接近原子的细节进行解释，并为过去和将来的功能研究提供令人兴奋的结构框架，从而使我们对复杂的转录起始过程具有独特的机械洞察力。
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