style="font-size:15px;"> Many innovative methods have been developed to mitigate pitfalls of these novel technologies: low efficiency can be enhanced by fusing the Cas proteins to more efficient nucleases (Dolan et al. 2019); specificity can be improved by careful crRNA design (Doench et al. 2016; Akcakaya et al. 2018) and enhanced by blocking unspecific sites (Coelho et al. 2020), the activity can be controlled by chemical agents (Maji et al. 2017) and optogenetically (Nihongaki et al. 2015). Whereas these tools are a powerful addition to the CRISPR arsenal, recently discovered inhibitors of CRISPR systems, the anti‐CRISPR proteins (Acr) provide the basis for even tighter control of undesired activities of Cas proteins (Davidson et al. 2020; Marino et al. 2020). Acrs are, in essence, an evolutionary response of mobile genetic elements able to inhibit CRISPR systems at various steps of the immune response. Just like CRISPR systems, their inhibitors are incredibly diverse, and thus represent yet another untapped resource of wonderful tools that can be used to further improve CRISPR editing, in particular in a therapeutic setting.
Studying the biology of diverse CRISPR systems did not lead just to the development of gene editing tools, but also ways to manipulate the transcriptome and the epigenome. Furthermore, by exploiting the seemingly undesirable collateral activity of type V and type VI systems, new molecular diagnostics tools with unprecedented detection sensitivity have been developed. Together, this diverse collection of novel ways to repurpose bacterial immune systems for a bespoke application is a witness of how much more we can get by understanding and studying microbial CRISPR systems. While class 2 systems have been studied (and hence appropriated for various applications) to a great extent, the application of class 1 systems is lagging. Furthermore, other phases of CRISPR immune response are still comparably poorly characterized, for example, adaptation phases. Studying these systems and these phases might well generate new powerful tools for genome editing or something completely different. One can only eagerly wait for what the next decades are going to bring.
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33 Cong,
