During the first step of gene expression, RNA polymerase (RNAP) engages DNA to transcribe RNA, forming highly stable complexes. These complexes need to be dissociated at the end of transcription units or when RNAP stalls during elongation and becomes an obstacle (‘sitting duck’) to further transcription or replication. In this review, we first outline the mechanisms involved in these processes. Then, we explore in detail the torpedo mechanism whereby a 5′–3′ RNA exonuclease (torpedo) latches itself onto the 5′ end of RNA protruding from RNAP, degrades it and upon contact with RNAP, induces dissociation of the complex. This mechanism, originally described in Eukaryotes and executed by Xrn-type 5′–3′ exonucleases, was recently found in Bacteria and Archaea, mediated by β-CASP family exonucleases. We discuss the mechanistic aspects of this process across the three kingdoms of life and conclude that 5′–3′ exoribonucleases (β-CASP and Xrn families) involved in the ancient torpedo mechanism have emerged at least twice during evolution.

中文翻译：

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从 DNA 中去除 RNA 聚合酶的 β-CASP 蛋白：当需要鱼雷射击坐鸭时

在基因表达的第一步，RNA 聚合酶 (RNAP) 与 DNA 结合以转录 RNA，形成高度稳定的复合物。这些复合物需要在转录单位末端或当 RNAP 在延伸过程中停滞并成为进一步转录或复制的障碍（“坐鸭”）时解离。在这篇综述中，我们首先概述了这些过程中涉及的机制。然后，我们详细探讨了鱼雷机制，其中 5'-3' RNA 外切酶（鱼雷）将自身锁定在从 RNAP 突出的 RNA 的 5' 端，降解它并在与 RNAP 接触时诱导复合物解离。这种机制最初在真核生物中描述并由 Xrn 型 5'-3' 核酸外切酶执行，最近在细菌和古细菌中发现，由 β-CASP 家族核酸外切酶介导。