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. Author manuscript; available in PMC: 2012 Jun 1.
Published in final edited form as: Curr Opin Microbiol. 2011 Apr 29;14(3):321–327. doi: 10.1016/j.mib.2011.03.005

Figure 3.

Figure 3

CRISPR-Cas systems of various prokaryotes include three co-evolved components: CRISPR repeats, CRISPR leaders, and associated Cas proteins that function on discrete PAMs (protospacer adjacent elements) present in the viruses and other mobile genetic elements that they encounter. Known and predicted interactions between Cas proteins and the host CRISPR RNA repeat sequences and leader DNA elements plus invader PAMs are indicated (arrows). The specificity of these RNA-protein and DNA-protein interactions likely contribute to the co-evolution of the four components.