Figure 7.

Model of pre-initiation, initiation and post-initiation states. The RNAP is shown in light blue, with the active site depicted as a white oval in the center. Nucleoprotein (NP) are shown in grey. The vRNA promoter is shown in orange, with base-paired residues in the duplex region highlighted in purple and incoming nucleoside triphosphates (NTPs) shown in green. Upon RNAP binding, the vRNA promoter exists in equilibrium between a pre-initiation state in which the 3′ RNA terminus is bound on the RNAP surface, and an initiation state in which the 3′ RNA is bound in the active site. In the presence of NTPs, the 3′ RNA starts to translocate through the active site during RNA synthesis, resulting in destabilization of the duplex region.