CRISPR-Cas起源：TnpB与IscB核酸酶的研究与应用进展

Origin of CRISPR-Cas: progress in research and applications of TnpB and IscB

摘要:

CRISPR-Cas系统是广泛存在于细菌和古菌中的防御系统。基于该系统开发的基因组编辑工具已在大量物种中实现靶向编辑。目前应用最多的是CRISPR-Cas9和CRISPR-Cas12a基因组编辑工具，但它们的蛋白大小均超过1 000个氨基酸，不利于递送。来自转座子家族的TnpB和IscB蛋白(大小约400个氨基酸)分别被认为是Cas12和Cas9的祖先蛋白，但其功能直到最近才被解析。它们被统称为专性移动元件引导活性(obligate mobile element-guided activity, OMEGA)蛋白，其引导RNA被称为ωRNA。此后，OMEGA系统成为了基因编辑领域的研究热点之一。OMEGA系统在三域生物中都有广泛分布，而且种类多样。对OMEGA系统的深入研究，将有助于开发精简、高效、安全的新型基因组编辑工具。本文围绕OMEGA系统的发现历程、结构特点、作用机制和在基因组编辑中的应用展开介绍，为新型基因组编辑工具的开发和优化提供参考。

Abstract:

CRISPR-Cas is a defense system ubiquitous in bacteria and archaea. It has been successfully applied in genome editing in a variety of organisms. At present, CRISPR-Cas9 and CRISPR-Cas12a are the most widely used genome editing tools. However, the large protein sizes of Cas9 and Cas12a (more than 1 000 amino acids (aa)) hinder their delivery. TnpB and IscB (about 400 aa) encoded by the transposon family are considered ancestors of Cas12 and Cas9, respectively, whereas their functions are revealed just recently. They are named as obligate mobile element-guided activity (OMEGA), with the associated RNA named ωRNA. Since then, the OMEGA system has become one of the research hotspots in genome editing. OMEGA systems are diverse, with wide distribution in all the three domains of life. The in-depth research on the OMEGA system will aid in the development of new genome editing tools that are streamlined, efficient, and safe. Here, we reviewed the discovery history, structural characteristics, mechanisms of cleavage, and genome editing applications of OMEGA systems, aiming to lay a foundation for the development and optimization of genome editing tools.