“…Class 1 is defined by multi-subunit CRISPR–Cas effector complexes, whereas Class 2 is characterized by single-subunit effector complexes (Koonin et al, 2017). Due to its simplicity, Class 2 is the easiest to be implemented in gene editing as well as manipulation of cell-free nucleic acids (Barrangou & Doudna, 2016; Gootenberg et al, 2017; Komor, Badran, & Liu, 2017; Koonin & Makarova, 2009; Lee et al, 2017; Wang, La Russa, & Qi, 2016). The Class 2 systems primarily include the Types II (Cas9), V (Cas12), and VI (Cas13) systems where Cas9 and Cas12 are RNA-guided DNA cleavage enzymes and Cas13 is RNA-guided RNA cleavage enzymes, although some DNA cleavage activities have been reported (Gao, Yang, Rajashankar, Huang, & Patel, 2016; Makarova, Zhang, & Koonin, 2017; Smargon et al, 2017).…”