Proofreading function associated with the RNA-dependent RNA polymerase from influenza virus.

The influenza virus-associated RNA polymerase cleaves capped RNA in an endonucleolytic manner and the transcription is initiated by the addition of GMP, the first substrate to be polymerized under the direction of viral RNA template, onto 3'-termini of resulting capped RNA fragments. In the presence of high concentrations of GTP as a sole substrate, multiple GMP residues were polymerized onto the primers. By the addition of the second substrate CTP, excess GMP residues, other than the 1st residue, were removed prior to elongation. The result may suggest that the RNA-dependent RNA polymerase carries a proofreading function.