CRISPR-Cas systems are a form of prokaryotic adaptive immunity that employs RNA-guided endonucleases (Cas effectors) to cleave foreign genetic elements. Due to their simplicity, targeting programmability, and efficiency, single-effector CRISPR-Cas systems have great potential for application in research, biotechnology, and therapeutics. While DNA-targeting Cas effectors such as Cas9 and Cas12a have become indispensable tools for genome editing in the past decade, the more recent discovery of RNA-targeting CRISPR-Cas systems has opened the door for implementation of CRISPR-Cas technology in RNA manipulation. With an increasing number of studies reporting their application in transcriptome engineering, viral interference, nucleic acid detection, and RNA imaging, type VI CRISPR-Cas systems and the associated Cas13 effectors particularly hold promise as RNA-targeting or RNA-binding tools. However, even though previous structural and biochemical characterization provided a firm basis for leveraging type VI CRISPR-Cas systems into such tools, the lack of comprehension of certain mechanisms underlying their functions hinders more sophisticated and conventional use. This review will summarize current knowledge on structural and mechanistic properties of type VI CRISPR-Cas systems, give an overview on the reported applications, and discuss functional features that need further investigation in order to improve performance of Cas13-based tools.

中文翻译：

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RNA靶向VI型CRISPR-Cas系统的功能特点和当前应用

CRISPR-Cas系统是原核适应性免疫的一种形式，它利用RNA引导的核酸内切酶（Cas效应子）来切割外源遗传元件。由于其简单性、靶向可编程性和效率，单效应器 CRISPR-Cas 系统在研究、生物技术和治疗领域具有巨大的应用潜力。虽然 Cas9 和 Cas12a 等 DNA 靶向 Cas 效应器在过去十年中已成为基因组编辑不可或缺的工具，但最近发现的 RNA 靶向 CRISPR-Cas 系统为在 RNA 操作中实施 CRISPR-Cas 技术打开了大门。随着越来越多的研究报告其在转录组工程、病毒干扰、核酸检测和 RNA 成像中的应用，VI 型 CRISPR-Cas 系统和相关的 Cas13 效应器尤其有望成为 RNA 靶向或 RNA 结合工具。然而，尽管之前的结构和生化表征为将 VI 型 CRISPR-Cas 系统利用到此类工具中提供了坚实的基础，但缺乏对其功能背后的某些机制的理解阻碍了更复杂和常规的使用。本综述将总结目前有关 VI 型 CRISPR-Cas 系统的结构和机械特性的知识，概述已报道的应用，并讨论需要进一步研究的功能特征，以提高基于 Cas13 的工具的性能。