FIG 13.

Reconstruction of quiescent ARV and binding changes in the terminal RNA during the priming process. (A and B) Asymmetric reconstruction of quiescent ARV; the TEC locations resemble those in primed ARV. (C) Magnified view of the boxed region in panel B to show a tropical TEC. (D to F) Structure comparison of RNA template entrances in the primed (D and E) and quiescent (F) states. The view in panel D is the same as that in Fig. 9A, except that the density maps of the terminal, side, and bound RNAs and the TEC are shown as shaded surfaces and as wire frames superimposed on the atomic models, respectively. The densities were low-pass filtered to facilitate comparison with the quiescent-ARV reconstruction. The terminal RNA bound to the CTD of NTPase in the quiescent state (F) detaches from the NTPase to bind H108 of the RdRp in the primed state (E). (G and H) Comparison of the cap-binding sites in primed ARV (G) and in the ORV λ3 crystal structure (PDB 1N1H) (H). Note that in primed ARV, the RNA 5′ cap is not bound to the cap-binding site.