小柯机器人

美国哥伦比亚大学Samuel H. Sternberg研究组发现，转座子编码的核酸酶利用向导RNA促进其自私传播。2023年9月27日，《自然》杂志在线发表了这项成果。

研究人员发现TnpB和IscB对于防止TnpA转座机制导致的永久性转座子丢失至关重要。研究人员从嗜热地芽孢杆菌（Geobacillus stearothermophilus）中选择了一系列相关的插入序列，这些序列编码多个TnpB和IscB同源物，结果表明单一的TnpA转座酶对转座子的调动具有广泛的活性。转座子侧翼序列重新连接后形成的供体接头被RNA引导的TnpB和IscB核酸酶有效地定向切割，与单独表达TnpA的条件相比，TnpB和TnpA的共同表达导致转座子保留率大大提高。值得注意的是，TnpA和TnpB还刺激了重组频率，超过了单独表达TnpB时的重组率。

总之，这项研究揭示了RNA引导的DNA切割是一种原始的生化活动，它偏向于转座元件的自私遗传和传播，后来在CRISPR-Cas适应性免疫的演化过程中被用于抗病毒防御。

据了解，插入序列是细菌中发现的紧凑而普遍的转座元件，它们只编码调动和维持转座元件所需的基因。IS200和IS605家族转座子在TnpA转座酶的催化下进行“剥离-粘贴”转座，但它们也编码多种TnpB和IscB家族蛋白，这些蛋白在演化上分别与CRISPR相关效应器Cas12和Cas9有关。最近的研究表明，TnpB和IscB具有RNA引导的DNA内切酶功能，但这种活性的更广泛生物学作用仍是个谜。

附：英文原文

Title: Transposon-encoded nucleases use guide RNAs to promote their selfish spread

Author: Meers, Chance, Le, Hoang C., Pesari, Sanjana R., Hoffmann, Florian T., Walker, Matt W. G., Gezelle, Jeanine, Tang, Stephen, Sternberg, Samuel H.

Issue&Volume: 2023-09-27

Abstract: Insertion sequences are compact and pervasive transposable elements found in bacteria, which encode only the genes necessary for their mobilization and maintenance1. IS200- and IS605-family transposons undergo ‘peel-and-paste’ transposition catalysed by a TnpA transposase2, but they also encode diverse, TnpB- and IscB-family proteins that are evolutionarily related to the CRISPR-associated effectors Cas12 and Cas9, respectively3,4. Recent studies have demonstrated that TnpB and IscB function as RNA-guided DNA endonucleases5,6, but the broader biological role of this activity has remained enigmatic. Here we show that TnpB and IscB are essential to prevent permanent transposon loss as a consequence of the TnpA transposition mechanism. We selected a family of related insertion sequences from Geobacillus stearothermophilus that encode several TnpB and IscB orthologues, and showed that a single TnpA transposase was broadly active for transposon mobilization. The donor joints formed upon religation of transposon-flanking sequences were efficiently targeted for cleavage by RNA-guided TnpB and IscB nucleases, and co-expression of TnpB and TnpA led to substantially greater transposon retention relative to conditions in which TnpA was expressed alone. Notably, TnpA and TnpB also stimulated recombination frequencies, surpassing rates observed with TnpB alone. Collectively, this study reveals that RNA-guided DNA cleavage arose as a primal biochemical activity to bias the selfish inheritance and spread of transposable elements, which was later co-opted during the evolution of CRISPR–Cas adaptive immunity for antiviral defence.

DOI: 10.1038/s41586-023-06597-1

Source: https://www.nature.com/articles/s41586-023-06597-1

Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
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