Second Messenger cA4 Formation within the Composite Csm1 Palm Pocket of Type III-A CRISPR-Cas Csm Complex and Its Release Path (Molecular Cell)

Cryo-EM and X-ray studies on type III-A CRISPR-Cas Csm ternary complexes bound to substrates (AMPPNP and ATP), intermediates (pppAn), and products (cAn) provide mechanistic insights into recognition of adenosine-specific substrates, positioning of linear pppAn intermediates, and subsequent cyclized cAn products, as well as an inter-subunit pathway for cAn products release.