The initiation of transcription is a focal point for the regulation of gene activity during mammalian cell differentiation and development. To initiate transcription, RNA polymerase II (Pol II) assembles with general transcription factors into a pre-initiation complex (PIC) that opens promoter DNA. Previous work provided the molecular architecture of the yeast^{1,2,3,4,5,6,7,8,9} and human^10,11 PIC and a topological model for DNA opening by the general transcription factor TFIIH^12,13,14. Here we report the high-resolution cryo-electron microscopy structure of PIC comprising human general factors and Sus scrofa domesticus Pol II, which is 99.9% identical to human Pol II. We determine the structures of PIC with closed and opened promoter DNA at 2.5–2.8 Å resolution, and resolve the structure of TFIIH at 2.9–4.0 Å resolution. We capture the TFIIH translocase XPB in the pre- and post-translocation states, and show that XPB induces and propagates a DNA twist to initiate the opening of DNA approximately 30 base pairs downstream of the TATA box. We also provide evidence that DNA opening occurs in two steps and leads to the detachment of TFIIH from the core PIC, which may stop DNA twisting and enable RNA chain initiation.

转录的起始是哺乳动物细胞分化和发育过程中基因活性调控的焦点。为了启动转录，RNA 聚合酶 II (Pol II) 与一般转录因子组装成一个启动前复合物 (PIC)，从而打开启动子 DNA。以前的工作提供了酵母^{1,2,3,4,5,6,7,8,9}和人类^{10,11 PIC 的分子结构以及通用转录因子 TFIIH 12,13,14}开放 DNA 的拓扑模型. 在这里，我们报告了 PIC 的高分辨率低温电子显微镜结构，包括人类一般因素和Sus scrofa domesticusPol II，与人类 Pol II 99.9% 相同。我们以 2.5-2.8 Å 的分辨率确定具有封闭和开放启动子 DNA 的 PIC 的结构，并以 2.9-4.0 Å 的分辨率解析 TFIIH 的结构。我们在易位前和易位后状态中捕获 TFIIH 易位酶 XPB，并表明 XPB 诱导和传播 DNA 扭曲以启动 TATA 盒下游约 30 个碱基对的 DNA 开放。我们还提供证据表明 DNA 开放分两个步骤发生，并导致 TFIIH 从核心 PIC 中脱离，这可能会阻止 DNA 扭曲并使 RNA 链启动。