A single amino acid mutation in the PA subunit of the influenza virus RNA polymerase promotes the generation of defective interfering RNAs.
Fodor E., Mingay LJ., Crow M., Deng T., Brownlee GG.
An R638A mutation of the polymerase acidic protein (PA) subunit of the RNA polymerase of influenza A/WSN/33 virus results in severe attenuation of viral growth in cell culture by promoting the synthesis of defective interfering RNAs. We propose that R638A is an "elongation" mutant that destabilizes PA-RNA template interactions during elongation. A C453R mutation in PA can compensate for this defect, suggesting that amino acids C453 and R638 form part of the same domain.