Fig. 4.

The affinity of the Dicer Platform + PAZ + Connector (PPC) domain for RNA targets increased independently in animal and plant lineages. We measured the binding kinetics of extant and ancestral-reconstructed Platform + PAZ + Connector domains to synthetic RNAs modeling endogenous microRNAs or viral-like RNA products (see Materials and Methods; RNA sequences are shown in supplementary fig. S10, Supplementary Material online). We plot steady-state binding (pKd, light bars) and initial binding rates (pKm, dark bars) to each RNA type, with longer bars indicating tighter binding. Standard errors are shown. Significant increases or decreases in RNA affinity along each branch on the simplified phylogeny are indicated by upward- or downward-pointing triangles, respectively (P < 0.05). Kinetics curves are shown in supplementary fig. S11, Supplementary Material online.