AlpA positively regulates a programmed cell death pathway linked to the virulence of Pseudomonas aeruginosa by recognizing an AlpA binding element within the promoter, then binding RNA polymerase directly and allowing it to bypass an intrinsic terminator positioned downstream. Here, we report the single-particle cryo-electron microscopy structures of both an AlpA-loading complex and an AlpA-loaded complex. These structures indicate that the C-terminal helix-turn-helix motif of AlpA binds to the AlpA binding element and that the N-terminal segment of AlpA forms a narrow ring inside the RNA exit channel. AlpA was also revealed to render RNAP resistant to termination signals by prohibiting RNA hairpin formation in the RNA exit channel. Structural analysis predicted that AlpA, 21Q, λQ and 82Q share the same mechanism of transcription antitermination.

中文翻译：

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AlpA依赖性转录抗终止的结构基础

AlpA 通过识别启动子内的 AlpA 结合元件，然后直接结合 RNA 聚合酶并使其绕过位于下游的内在终止子，正向调节与铜绿假单胞菌毒力相关的程序性细胞死亡途径。在这里，我们报告了装载 AlpA 的复合物和装载 AlpA 的复合物的单粒子低温电子显微镜结构。这些结构表明AlpA的C端螺旋-转角-螺旋基序与AlpA结合元件结合，并且AlpA的N端片段在RNA出口通道内形成一个窄环。AlpA 还被发现通过阻止 RNA 出口通道中的 RNA 发夹形成来使 RNAP 对终止信号具有抗性。结构分析预测AlpA、21Q、λQ和82Q具有相同的转录抗终止机制。