Cas9 is a bacterial immune protein that destroys invading DNA. A guide RNA holds the address, and the protein holds two nuclease domains that cut the two DNA strands. The guide RNA loads first and swings the two protein lobes into a channel that accepts DNA. The address sits in the RNA, not in the protein, so one enzyme reaches any sequence.
1368
One polypeptide. The largest single-chain machine in this atlas.
158 kDa
2
HNH cuts the strand complementary to the guide. The RuvC-like domain cuts the other strand.
D10 and H840
Asp10 serves the RuvC-like site. His840 is the proton acceptor of the HNH site.
NGG
The protospacer adjacent motif. It limits which sites the enzyme can reach. Arg1333 and Arg1335 read its two guanines.
82-118 nucleotides
Guide RNA length in these structures
7Single-guide RNAs of 82 to 118 nt across the deposited entries used here.
27.5 A CA rmsd
Lobe reorientation on guide loading
4Measured in this work: best-fit superposition of chain A of apo 4CMP on chain A of guide-bound 4ZT0, over 1126 shared residues.
22.0 to 3.3 A
HNH approach to the cut site
11Measured in this work: closest distance from residue 840 to the target DNA strand, 22.0 A in 6O0Z and 3.3 A in 6O0Y.