Ⅰ型CRISPR-Cas系统效应物的结构特征及其在基因编辑领域的应用

Structural feature of type Ⅰ CRISPR-Cas system and its application in gene editing

CRISPR-Cas(clustered regularly interspaced short palindromic repeats and CRISPR-associated)系统是在细菌和古细菌基因组中发现的一种由RNA介导、抵挡外源核酸入侵的适应性免疫系统。通过对靶标位点的特异性识别,结合细胞自身的DNA修复功能或转录调控机制,CRISPR-Cas系统可高效编辑靶标序列或精准调控基因的表达,目前已被开发成为基因编辑领域的有力工具。根据效应复合物组成形式的不同,CRISPR-Cas系统分为1类(Ⅰ型、Ⅳ型和Ⅲ型)和2类(Ⅱ型、Ⅴ型和Ⅵ型)两大类。2类中的CRISPR-Cas9系统作为最早发现且被研究透彻的系统之一,应用范围已十分广泛;而1类系统虽占整个CRISPR-Cas系统的90%,但目前还未有开发成熟的应用工具。本综述以1类中的Ⅰ型系统为例,从亚型分类、效应复合物组装与结构、Cas3蛋白的切割降解机制以及近几年在基因编辑中的应用等方面进行总结,为更好地研究该类别的作用机制及后期的开发应用提供新的思路和方法。

The CRISPR-Cas(clustered regularly interspaced short palindromic repeats and CRISPR-associated)system is an "adaptive immune system" found in the genomes of bacteria and archaea which is mediated by RNA and resists foreign nucleic acid invasion. Take advantage of specific recognition of target nucleic acid, CRISPRCas system can efficiently edit their target site or accurately regulate gene expression, and now have been developed into a powerful tool for gene editing. According to the different compositions of the effector complex, the system has been divided into two categories: class 1(type Ⅰ, type Ⅳ, and type Ⅲ) and class 2(type Ⅱ, type Ⅴ, and type Ⅵ). Class 2 system, like the CRISPR-Cas9, is widely used in basic research due to the earliest discovery and best research. However, class 1 has not been maturely developed and utilized though it makes up 90% of the entire CRISPR-Cas system. In this essay, the classification of subtype, the assembly of Cascade complex, the cleavage and degradation mechanism of Cas3, and the application in gene editing of class 1 type I CRISPR-Cas system will be discussed and summarized to provide new ideas and methods for further mechanism studying and application of this category.