Molecular basis for RNA polymerization by Qß replicase.

Core Qß replicase comprises the Qß virus-encoded RNA-dependent RNA polymerase (ß-subunit) and the host Escherichia coli translational elongation factors EF-Tu and EF-Ts. The functions of the host proteins in the viral replicase are not clear. Structural analyses of RNA polymerization by core Qß replicase reveal that at the initiation stage, the 3'-adenine of the template RNA provides a stable platform for de novo initiation. EF-Tu in Qß replicase forms a template exit channel with the ß-subunit. At the elongation stages, the C-terminal region of the ß-subunit, assisted by EF-Tu, splits the temporarily double-stranded RNA between the template and nascent RNAs before translocation of the single-stranded template RNA into the exit channel. Therefore, EF-Tu in Qß replicase modulates RNA elongation processes in a distinct manner from its established function in protein synthesis.