Medizinische Physik und Biophysik, Charité - Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany.
Freie Universität Berlin, Laboratory of Structural Biochemistry, Takustraβe 6, 14195 Berlin, Germany.
Mol Cell. 2019 Apr 4;74(1):143-157.e5. doi: 10.1016/j.molcel.2019.01.016. Epub 2019 Feb 19.
Bacteriophage λN protein, a model anti-termination factor, binds nascent RNA and host Nus factors, rendering RNA polymerase resistant to all pause and termination signals. A 3.7-Å-resolution cryo-electron microscopy structure and structure-informed functional analyses reveal a multi-pronged strategy by which the intrinsically unstructured λN directly modifies RNA polymerase interactions with the nucleic acids and subverts essential functions of NusA, NusE, and NusG to reprogram the transcriptional apparatus. λN repositions NusA and remodels the β subunit flap tip, which likely precludes folding of pause or termination RNA hairpins in the exit tunnel and disrupts termination-supporting interactions of the α subunit C-terminal domains. λN invades and traverses the RNA polymerase hybrid cavity, likely stabilizing the hybrid and impeding pause- or termination-related conformational changes of polymerase. λN also lines upstream DNA, seemingly reinforcing anti-backtracking and anti-swiveling by NusG. Moreover, λN-repositioned NusA and NusE sequester the NusG C-terminal domain, counteracting ρ-dependent termination. Other anti-terminators likely utilize similar mechanisms to enable processive transcription.
噬菌体 λN 蛋白是一种模型抗终止因子，可结合新生 RNA 和宿主 Nus 因子，使 RNA 聚合酶对所有暂停和终止信号具有抗性。3.7Å 分辨率的冷冻电镜结构和结构导向的功能分析揭示了 λN 蛋白的一种多管齐下的策略，该策略通过固有无结构的 λN 蛋白直接修饰 RNA 聚合酶与核酸的相互作用，并颠覆 NusA、NusE 和 NusG 的基本功能，从而重新编程转录装置。λN 重新定位 NusA 并重塑β亚基瓣尖端，这可能阻止了在出口隧道中形成暂停或终止 RNA 发夹，并破坏了α亚基 C 末端结构域的终止支持相互作用。λN 侵入并穿过 RNA 聚合酶杂交腔，可能稳定杂交体并阻碍与暂停或终止相关的聚合酶构象变化。λN 还沿着上游 DNA 排列，似乎通过 NusG 加强反回溯和反旋转。此外，重新定位的 NusA 和 NusE 将 NusG C 末端结构域隔离，抵消 ρ 依赖性终止。其他抗终止因子可能利用类似的机制来实现连续转录。
