Ⅰ-E型CRISPR/Cas系统介导适应性免疫分子机制研究进展

Advances in molecular mechanisms of adaptive immunity mediated by type Ⅰ-E CRISPR/Cas system- A review

为了更好地适应环境,原核生物可通过水平基因转移的方式获取外源基因(来自噬菌体、质粒或其他物种基因组)。在获取外源基因的同时,原核生物也面临着"自私基因"入侵的风险。因此,原核生物需建立相应的机制选择性地摄取或降解外源DNA,从而防范基因转移带来的潜在危害。近年来,人们在原核生物中发现了由小RNA介导降解DNA的防御外源基因入侵的适应性免疫。在免疫防御过程中,首先外源DNA部分片段整合至细胞自身基因组上成簇出现的重复序列(CRISPR)上;然后表达并加工成熟的CRISPR RNA和相关Cas蛋白形成CRISPR/Cas复合体降解再次入侵的外源DNA。本文在简介CRISPR/Cas系统的基础上,重点探讨近年来关于大肠杆菌中I-E型CRISPR/Cas系统作用机制和调控机制的研究进展。

To better adapt to the environment, prokaryocyte can take up exogenous genes（from bacteriophages, plasmids or genomes of other species） through horizontal gene transfer. Accompanied by the acquisition of exogenous genes,prokaryocyte is challenged by the invasion of ‘selfish genes＇. Therefore, to protect against the risk of gene transfer,prokaryocyte needs to establish mechanisms for selectively taking up or degrading exogenous DNA. In recent years,researchers discovered an adaptive immunity, which is mediated by the small RNA guided DNA degradation, prevents the invasion of exogenous genes in prokaryocyte. During the immune process, partial DNA fragments are firstly integrated to the clustered regularly interspaced short palindromic repeats（CRISPR） located within the genome DNA, and then the mature CRISPR RNA transcript and the CRISPR associated proteins（Cas） form a complex CRISPR/Cas for degrading exogenous DNA. In this review, we will first briefly describe the CRISPR/Cas systems and then mainly focus on the recent advances of the function mechanism and the regulation mechanism of the type I-E CRISPR/Cas system in Escherichia coli.