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. Author manuscript; available in PMC: 2020 Feb 1.
Published in final edited form as: EcoSal Plus. 2019 Feb;8(2):10.1128/ecosalplus.ESP-0008-2018. doi: 10.1128/ecosalplus.ESP-0008-2018

Figure 6.

Figure 6.

Expression and maturation of crRNAs and assembly of Cascade and Csy surveillance complexes. A. The product of transcription of the CRISPR is a pre-crRNA containing stem-loops within the repeats. Cas6 endoribonucleases (pink) recognize the stem-loops and cleave at the base to form mature crRNAs. B. Cas6 subunits remain bound to the stem-loop at the 3’-end of the crRNA following cleavage. Six Cas7 subunits (blue) assemble along the length of the crRNA spacer (red), and the Cas5 subunit (purple) caps the Cas7 backbone by specifically recognizing the 5’-repeat-derived handle. In type I-E Cascade, two subtype-specific subunits, Cse2 (orange), assemble on the belly of the complex. The Cas8 subunit (green) caps the complex on the Cas5 end. C. Schematic of assembled Cascade (C) or Csy (D) complex. Subunits are colored as in B, except for Cas8e (C) or Cas8f (D), which are shown in green outline. E-F. Structures of fully assembled E. coli Cascade (PDB ID 4TVX) and P. aeruginosa Csy (PDB ID 6B45) complex (59, 120).