转录起始复合物在分歧启动子上的结构基础。
Structural basis of a transcription pre-initiation complex on a divergent promoter.
机构信息
Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA; Biochemistry and Molecular Biophysics Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Department of Biochemistry and Molecular Biology, McGovern Medical School, University of Texas Health Science Center at Houston, Houston, TX 77030, USA.
出版信息
Mol Cell. 2023 Feb 16;83(4):574-588.e11. doi: 10.1016/j.molcel.2023.01.011. Epub 2023 Feb 1.
Most eukaryotic promoter regions are divergently transcribed. As the RNA polymerase II pre-initiation complex (PIC) is intrinsically asymmetric and responsible for transcription in a single direction, it is unknown how divergent transcription arises. Here, the Saccharomyces cerevisiae Mediator complexed with a PIC (Med-PIC) was assembled on a divergent promoter and analyzed by cryoelectron microscopy. The structure reveals two distinct Med-PICs forming a dimer through the Mediator tail module, induced by a homodimeric activator protein localized near the dimerization interface. The tail dimer is associated with ∼80-bp upstream DNA, such that two flanking core promoter regions are positioned and oriented in a suitable form for PIC assembly in opposite directions. Also, cryoelectron tomography visualized the progress of the PIC assembly on the two core promoter regions, providing direct evidence for the role of the Med-PIC dimer in divergent transcription.
大多数真核生物启动子区域是反向转录的。由于 RNA 聚合酶 II 起始前复合物（PIC）本质上是不对称的，只能沿一个方向转录，因此尚不清楚如何产生反向转录。在这里，与 PIC 复合的酿酒酵母 Mediator（Med-PIC）被组装在一个反向转录的启动子上，并通过冷冻电子显微镜进行分析。该结构揭示了两个通过 Mediator 尾部模块形成二聚体的独特 Med-PIC，这是由位于二聚化界面附近的同源二聚体激活蛋白诱导的。尾部二聚体与约 80bp 的上游 DNA 结合，使得两个侧翼的核心启动子区域以适合 PIC 沿相反方向组装的形式定位和定向。此外，冷冻电子断层扫描可视化了 PIC 在两个核心启动子区域上的组装过程，为 Med-PIC 二聚体在反向转录中的作用提供了直接证据。
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