Figure 1. Crystal Structure of the SthCsm Complex.
(A) Schematic view of a type III-A CRISPR-Cas system in S. thermophilus.
(B) The overall structure of the SthCsm complex associated with a crRNA. Color coding used for Csm1–Csm5 is identical to that used in (A). The spacer and 5′ tag regions of crRNA are in red and gray, respectively.
(C) The schematic representation of Csm1 domains. The HD, Palm1, Linker, Palm2, and D4 domains are shown in cyan, orange, purple, salmon, and wheat, respectively.
(D) Structure of Csm1 subunit in the same orientation as in (B).
(E) Close-up view of the crRNA spacer region and Csm3 β-thumb. The β-thumb of each Csm3 subunit folds over the top of the crRNA, creating a kink in the crRNA at 6-nt interval.
(F) Magnified view of the interactions between nucleotides (−6)–(−8) and the Csm1-Csm4 subcomplex illustrates that nucleotides (−6)–(−7) are sequence specifically recognized by Csm1 and Csm4 subunits.
(G) The target RNA dependent non-specific DNA cleavage with either Csm4 or Csm1 mutant form.
(H) Interactions between the nucleotides (−2)–(−5) of crRNA and Csm4-Csm3.1 subcomplex showing that these nucleotides are solvent exposed.