Fig. 3 |. Structures of RdRp and capped-terminal RNA in the quiescent and initiation states.

a–g, Structures of RdRp with capped-terminal RNA, in quiescent (a–c) and initiation (d–g) states. The non-template RNA binding cleft is boxed in black solid squares in b and e, and is magnified in c and f. In g, only the model of m⁷GpppA is shown, with the RNA chain hidden to better reveal the cap binding site underneath the non-template RNA binding cleft. h, Magnified views of the area in the dotted red square in b and e. Electrostatic surface renderings show the template RNA entry channel in the quiescent (upper) and initiation (lower) states. i, Magnified and rotated view of the area in the solid black square in d, with the density (semi-transparent grey) and atomic model (colored sticks) of the initial template-transcript complex inside the polymerase core shown alongside the ribbon model of the RdRp. The priming loop (red) of the RdRp and Mg²+ (green balls) are highlighted. j, Comparison of the priming loop in both the quiescent and initiation states.