Figure 10.

(a) Secondary structure of the Azoarcus ribozyme consisting of four different strands of RNA, W, X, Y, and Z. Self-replication is mediated by recognition of the target sites by the IGS (grey boxes), leading to ligation of the strands. The dashed line indicates the catalytic core of the resulting ribozyme. (b) Cooperative replicating system. The formation of the covalent ribozyme E3 from the non-covalent I3 complex is catalyzed by E2 ribozyme. The formation of this E2 is in turn catalyzed by E1, which is catalyzed by E3, resulting in a cyclic dependence. Numbers above the arrows denote the advantage of cooperativity [46].