Structures of Cas9 Endonucleases Reveal RNA-Mediated Conformational Activation

摘要

Bacteria and archaea defend themselves against invasive DNA using adaptive immune systems comprising CRISPR (clustered regularly interspaced short palindromic repeats) loci and CRISPR-associated (Cas) genes. In association with Cas proteins, small CRISPR RNAs (crRNAs) guide the detection and cleavage of complementary DNA sequences. Type Ⅱ CRISPR systems employ the RNA-guided endonuclease Cas9 to recognize and cleave double-stranded DNA (dsDNA) targets using conserved RuvC and HNH nuclease domains. Cas9-mediated cleavage is strictly dependent on the presence of a protospacer adjacent motif (PAM) in the target DNA. Recently, the biochemical properties of Cas9-guide RNA complexes have been harnessed for various genetic engineering applications and RNA-guided tran-scriptional control. Despite these ongoing successes, the structural basis for guide RNA recognition and DNA targeting by Cas9 is still unknown.