Structural basis for the fast self-cleavage reaction catalyzed by the twister ribozyme

Twister is a small self-cleaving ribozyme similar in size to the hammerhead ribozyme but uses an orthogonal fold for a similar catalytic rate constant. However, the mechanistic source of the catalytic rate increase generated by twister was unknown. We present crystal structures of twister from Orzyza sativa as well as a twister sequence from an organism that has not been cultured in isolation and identify RNA nucleotides that are vital for self-cleavage, suggest their catalytic roles, and update twister's conserved secondary structure model.