Cryo-EM structures of Escherichia coli transcription-translation complexes reveal how bacterial transcription and translation are coupled. Coupling transcription and translation In bacteria, the rate of transcription of messenger RNA (mRNA) by RNA polymerase (RNAP) is coordinated with the rate of translation by the first ribosome behind RNAP on the mRNA. Two groups now present cryo–electron microscopy structures that show how two transcription elongation factors, NusG and NusA, participate in this coupling. Webster et al. found that NusG forms a bridge between RNAP and the ribosome when they are separated by mRNA. With shortened mRNA, NusG no longer links RNAP and the ribosome, but the two are oriented so that newly transcribed mRNA can enter the ribosome. Wang et al. provide further insight into the effect of mRNA length on the complex structures. They also include NusA and show that the NusG-bridged structure is stabilized by NusA. Science, this issue p. 1355, p. 1359 Prokaryotic messenger RNAs (mRNAs) are translated as they are transcribed. The lead ribosome potentially contacts RNA polymerase (RNAP) and forms a supramolecular complex known as the expressome. The basis of expressome assembly and its consequences for transcription and translation are poorly understood. Here, we present a series of structures representing uncoupled, coupled, and collided expressome states determined by cryo–electron microscopy. A bridge between the ribosome and RNAP can be formed by the transcription factor NusG, which stabilizes an otherwise-variable interaction interface. Shortening of the intervening mRNA causes a substantial rearrangement that aligns the ribosome entrance channel to the RNAP exit channel. In this collided complex, NusG linkage is no longer possible. These structures reveal mechanisms of coordination between transcription and translation and provide a framework for future study.

中文翻译：

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细菌转录-翻译耦合与碰撞的结构基础

大肠杆菌转录-翻译复合物的冷冻电镜结构揭示了细菌转录和翻译是如何耦合的。偶联转录和翻译 在细菌中，RNA 聚合酶 (RNAP) 对信使 RNA (mRNA) 的转录速率与 RNAP 后第一个核糖体对 mRNA 的翻译速率相协调。两组现在展示了低温电子显微镜结构，显示了两个转录延伸因子 NusG 和 NusA 如何参与这种耦合。韦伯斯特等人。发现当它们被 mRNA 分开时，NusG 在 RNAP 和核糖体之间形成了一座桥梁。随着 mRNA 的缩短，NusG 不再连接 RNAP 和核糖体，而是将两者定向，以便新转录的 mRNA 可以进入核糖体。王等人。进一步深入了解 mRNA 长度对复杂结构的影响。它们还包括 NusA，并表明 NusG 桥接结构由 NusA 稳定。科学，本期第 3 页。第 1355 页，第 1359 个原核信使 RNA (mRNA) 在转录时被翻译。先导核糖体可能与 RNA 聚合酶 (RNAP) 接触并形成称为表达组的超分子复合物。表达组组装的基础及其对转录和翻译的影响知之甚少。在这里，我们提出了一系列结构，代表了由冷冻电子显微镜确定的非耦合、耦合和碰撞表达组状态。核糖体和 RNAP 之间的桥梁可以由转录因子 NusG 形成，它可以稳定原本可变的相互作用界面。中间 mRNA 的缩短导致大量重排，使核糖体入口通道与 RNAP 出口通道对齐。在这个碰撞的复合体中，NusG 连接不再可能。这些结构揭示了转录和翻译之间的协调机制，并为未来的研究提供了框架。