Abstract
The class II clustered regularly interspaced short palindromic repeats (CRISPR)–Cas systems, characterized by a single effector protein, can be further subdivided into types II, V, and VI. The application of the type II CRISPR effector protein Cas9 as a sequence-specific nuclease in gene editing has revolutionized this field. Similarly, Cas13 as the effector protein of type VI provides a convenient tool for RNA manipulation. Additionally, the type V CRISPR–Cas system is another valuable resource with many subtypes and diverse functions. In this review, we summarize all the subtypes of the type V family that have been identified so far. According to the functions currently displayed by the type V family, we attempt to introduce the functional principle, current application status, and development prospects in biotechnology for all major members.
Highlights
The clustered regularly interspaced short palindromic repeats (CRISPR)–Cas (CRISPR-associated protein) system is an acquired immune mechanism, mostly found in bacteria and archaea as a defense against environmental mobile genetic elements (MGEs), such as phages, plasmids, and transposons (Sorek et al, 2013; Koonin et al, 2017)
After the effector protein binds the guide RNA (gRNA) to form a binary complex, it recognizes the 5′ T-rich protospacer-adjacent motif (PAM) and promotes target DNA unwinding, specified by Watson–Crick base pairing with the guide sequence of CRISPR RNA (crRNA) (Stella et al, 2017)
The mature tracrRNA and crRNA were obtained through environmental meta-transcriptomic sequence analysis. When these genes were expressed in a heterologous host, Cas14 could successfully bind the gRNA to form a binary complex, no catalytic activity was observed with either single- or double-stranded DNA or RNA in vivo
Summary
The CRISPR (clustered regularly interspaced short palindromic repeats)–Cas (CRISPR-associated protein) system is an acquired immune mechanism, mostly found in bacteria and archaea as a defense against environmental mobile genetic elements (MGEs), such as phages, plasmids, and transposons (Sorek et al, 2013; Koonin et al, 2017). This is significantly different from the type II CRISPR enzyme Cas9, which uses the HNH-nuclease domain and RuvC-like nuclease domain to cut the two strands of the targeted DNA segment, respectively (Sternberg et al, 2015). Most of the CRISPR systems identified as belonging to the type V family have demonstrated targeted RNA-guided dsDNA cleavage activity.
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