Fig. 1.
A unique EV71 RdRP EC crystal lattice allows multiple nucleotide-incorporation events. (A) 2Fo-Fc electron density map (contoured at 1.5 σ with a radius of 30 Å, in cyan) around the upstream end of one EC (polymerase in green, RNA strands in red and blue) shows a spacious channel to accommodate the growth of RNA duplex. The black dot indicates the center of the map, and symmetry-related neighboring ECs are labeled as Sym1/2/3. (B) RNA sequence flanking the active site of the native EC (C1S1) and those of the other six complexes derived from the native EC in crystal-soaking trials. The template is in cyan, and product is in green. The black box indicates the nucleotides incorporated during soaking. “C” and “S” in complex names stand for “cycle” and “state,” respectively, and the subscript numbers reflect the assigned cycle/state numbers. (C) The isomorphous nature of the EC lattices. C1S1/2 and C3S6 structures (bold-faced in B) were chosen as representatives to indicate the very limited lattice alteration upon three rounds of nucleotide incorporation. The superimposed polymerases (using the traditional least-squares method) are on the right side with the C1S1/2 complex taking a coloring scheme indicated by individual parts of the EC and the C3S6 complex in black; their symmetry-related neighboring ECs are colored in orange (C1S1/2) and purple (C3S6).