美国普渡大学Leifu Chang小组宣布他们提出了dCas12f-σ^E-RNAP复合物介导RNA转录的结构基础。该研究于2026年3月4日发表于国际一流学术期刊《自然》杂志上。

本研究通过对中国鞭毛单胞菌dCas12f-σ^E系统的低温电镜结构分析，揭示了一种RNA引导转录起始的新模式。研究组捕获了多种构象和组成状态，包括DNA结合的dCas12f -σ^E-RNAP全酶复合物，揭示了RNA引导的DNA结合如何在r环下游精确定义的距离上导致σ^E-RNAP招募和新生mRNA合成。不同于经典的σ^E相关启动子识别范式，这些研究表明35元素在很大程度上被CRISPR-Cas靶向所取代，而融化的10元素通过非自然堆叠相互作用而不是插入到典型的识别口袋中来稳定。总的来说，这项工作为RNA引导转录的意想不到的机制提供了高分辨率的见解，扩大了他们对细菌基因调控的理解，并为可编程转录控制开辟了新的途径。

研究人员表示，在自然和工程生物系统中，RNA引导蛋白通过调节RNA聚合酶（RNAP）及其相关因子而成为关键的转录调节因子。在细菌中，多种重组TnpB和CRISPR相关蛋白分支通过阻断转录起始或延伸来抑制基因表达，从而实现非规范的调控模式和适应性免疫。一种独特的核酸酶死亡Cas12f同源物（dCas12f）通过与独特的胞质外功能σ因子（σ^E）的关联来激活基因表达，尽管分子基础仍然是未知的。

附：英文原文

Title: Structural basis of RNA-guided transcription by a dCas12f–σE–RNAP complex

Author: Xiao, Renjian, Hoffmann, Florian T., Xie, Dan, Wiegand, Tanner, Palmieri, Adriana I., Sternberg, Samuel H., Chang, Leifu

Issue&Volume: 2026-03-04

Abstract: In both natural and engineered biological systems, RNA-guided proteins have emerged as critical transcriptional regulators by modulating RNA polymerase (RNAP) and its associated factors1,2,3. In bacteria, diverse clades of repurposed TnpB and CRISPR-associated proteins repress gene expression by blocking transcription initiation or elongation, enabling non-canonical modes of regulatory control and adaptive immunity1,4,5. A distinct class of nuclease-dead Cas12f homologues (dCas12f) instead activates gene expression through its association with unique extracytoplasmic function sigma factors (σE)6, although the molecular basis has remained elusive. Here we reveal a new mode of RNA-guided transcription initiation by determining the cryo-electron microscopy structures of the dCas12f–σE system from Flagellimonas taeanensis. We captured multiple conformational and compositional states, including the DNA-bound dCas12f–σE–RNAP holoenzyme complex, revealing how RNA-guided DNA binding leads to σE–RNAP recruitment and nascent mRNA synthesis at a precisely defined distance downstream of the R-loop. Rather than following the classical paradigm of σE-dependent promoter recognition, these studies show that recognition of the 35 element is largely supplanted by CRISPR–Cas targeting, whereas the melted 10 element is stabilized through unusual stacking interactions rather than insertion into the typical recognition pocket. Collectively, this work provides high-resolution insights into an unexpected mechanism of RNA-guided transcription, expanding our understanding of bacterial gene regulation and opening new avenues for programmable transcriptional control.

DOI: 10.1038/s41586-026-10178-3

Source: https://www.nature.com/articles/s41586-026-10178-3