“…Type VI CRISPR-Cas systems include a single protein, Cas13 (formerly C2c2), that when assembled with a CRISPR-RNA (crRNA) forms a crRNA-guided RNA-targeting effector complex (Abudayyeh et al, 2016; East-Seletsky et al, 2016; Konermann et al, 2018; Shmakov et al, 2015; Smargon et al, 2017; Yan et al, 2018). Cas13 proteins are classified into distinct subfamilies (Cas13a-d), and all Cas13 proteins studied to date possess two enzymatically distinct RNase activities that are required for optimal interference (Abudayyeh et al, 2016; East-Seletsky et al, 2016; Konermann et al, 2018; Smargon et al, 2017; Yan et al, 2018). First, upon binding a precursor-crRNA (pre-crRNA), Cas13 cleaves within the crRNA direct repeat in a pre-crRNA array to form mature Cas13-crRNA complexes (East-Seletsky et al, 2016; East-Seletsky et al, 2017; Konermann et al, 2018; Smargon et al, 2017; Yan et al, 2018).…”