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Table 1 Major components of each CRISPR typea

From: Application of CRISPR/Cas9 for biomedical discoveries

Action Type I Type II Type III
Spacer acquisition Cas1/Cas2 Cas1/Cas2/Csn1/Cas9 Cas1/Cas2
Pre-cRNAprocessing Cas6 or Cas5 Rnase III Cas6
Interference Complex members Cascade tracrRNA/Cas9 Csm/Cmr
Secondary processing None 5′ end cleavage 3′ end cleavage
Interference Subtubes I-A, I-B, I-E, I-F, I-C, II-A, II-B, II-C III-A, III-B
  1. aCRISPR types are characterized by their operon composition the involved Cas proteins and the structure of the repeats in the CRISPR array. This table presents the defining characteristics of each type [27, 28]. Cascade = CRISPR-associated complex for antiviral defense