小柯机器人

美国康奈尔大学Joseph E. Peters课题组发现，向导RNA分类使Tn7-CRISPR-Cas转座子的靶点位点选择成为可能。2020年12月2日，《细胞》杂志在线发表了这项成果。

据研究人员介绍，CRISPR-Cas防御系统在自然界已被多次用于通过Tn7样元件来指导RNA定向转座。原型Tn7将专用蛋白用于两种靶向途径：一种靶向染色体中的中性和保守的附着位点，另一种靶向转座到可促进细胞间转移的移动质粒中。

研究人员发现，Tn7-CRISPR-Cas元件进化出了一种向导RNA分类的系统，从而能够实现相同两种途径的工作方式。多种机制使得功能不同的向导RNA进行转座：常规系统能够获取引导至新质粒和噬菌体靶标的引导RNA，而第二种系统则可在进入新宿主后为进入染色体位点提供长期记忆。向导RNA被私有化后只能通过转座子适应系统通过序列特化、错配耐受性和选择性调节来识别，以避免内源CRISPR-Cas防御系统进行有毒的自我靶向。

该信息揭示了有前景的途径来工程指导RNA从而增强CRISPR-Cas功能以进行基因组修饰。

附：英文原文

Title: Guide RNA Categorization Enables Target Site Choice in Tn7-CRISPR-Cas Transposons

Author: Michael T. Petassi, Shan-Chi Hsieh, Joseph E. Peters

Issue&Volume: 2020-12-02

Abstract: CRISPR-Cas defense systems have been coopted multiple times in nature for guide RNA-directedtransposition by Tn7-like elements. Prototypic Tn7 uses dedicated proteins for twotargeting pathways: one targeting a neutral and conserved attachment site in the chromosomeand a second directing transposition into mobile plasmids facilitating cell-to-celltransfer. We show that Tn7-CRISPR-Cas elements evolved a system of guide RNA categorizationto accomplish the same two-pathway lifestyle. Multiple mechanisms allow functionallydistinct guide RNAs for transposition: a conventional system capable of acquiringguide RNAs to new plasmid and phage targets and a second providing long-term memoryfor access to chromosomal sites upon entry into a new host. Guide RNAs are privatizedto be recognized only by the transposon-adapted system via sequence specialization,mismatch tolerance, and selective regulation to avoid toxic self-targeting by endogenousCRISPR-Cas defense systems. This information reveals promising avenues to engineerguide RNAs for enhanced CRISPR-Cas functionality for genome modification.

DOI: 10.1016/j.cell.2020.11.005

Source: https://www.cell.com/cell/fulltext/S0092-8674(20)31464-1