Reverse transcriptases (RTs) catalyze the polymerization of DNA from an RNA template. These enzymes were first discovered in RNA tumor viruses in 1970, but it was not until 1989 that they were found in prokaryotes as a key component of retrons. Apart from RTs encoded by the “selfish” mobile retroelements known as group II introns, prokaryotic RTs are extraordinarily diverse, but their function has remained elusive. However, recent studies have revealed that different lineages of prokaryotic RTs, including retrons, those associated with CRISPR-Cas systems, Abi-like RTs, and other yet uncharacterized RTs, are key components of different lines of defense against phages and other mobile genetic elements. Prokaryotic RTs participate in various antiviral strategies, including abortive infection (Abi), in which the infected cell is induced to commit suicide to protect the host population, adaptive immunity, in which a memory of previous infection is used to build an efficient defense, and other as yet unidentified mechanisms. These prokaryotic enzymes are attracting considerable attention, both for use in cutting-edge technologies, such as genome editing, and as an emerging research topic. In this review, we discuss what is known about prokaryotic RTs, and the exciting evidence for their domestication from retroelements to create specialized defense systems.

中文翻译：

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原核逆转录酶：从逆转录元件到专门的防御系统


逆转录酶 (RT) 催化 RNA 模板的 DNA 聚合。这些酶于 1970 年首次在 RNA 肿瘤病毒中发现，但直到 1989 年才在原核生物中作为逆转录子的关键成分被发现。除了由被称为第二组内含子的“自私”移动逆转录元件编码的 RT 之外，原核 RT 非常多样化，但它们的功能仍然难以捉摸。然而，最近的研究表明，不同谱系的原核 RT，包括反转录子、与 CRISPR-Cas 系统相关的 RT、Abi 样 RT 和其他尚未表征的 RT，是针对噬菌体和其他移动遗传元件的不同防线的关键组成部分。原核 RT 参与各种抗病毒策略，包括流产感染 (Abi)，其中受感染的细胞被诱导自杀以保护宿主群体；适应性免疫，其中利用先前感染的记忆来建立有效的防御；以及其他尚未确定的机制。这些原核酶吸引了相当多的关注，既用于基因组编辑等尖端技术，又作为新兴的研究课题。在这篇综述中，我们讨论了关于原核 RT 的已知信息，以及从逆转录因子驯化它们以创建专门的防御系统的令人兴奋的证据。