Differential activation of influenza A virus endonuclease activity is dependent on multiple sequence differences between the virion RNA and cRNA promoters.

Influenza virus endonuclease activity was studied in vitro with model virion RNA (vRNA) and cRNA molecules. We show that endonuclease activity can be partially rescued by transplanting vRNA-like promoter features into the model cRNA promoter. This study defines three distinctive features within the vRNA promoter--absent in the cRNA promoter--that are required for endonuclease cleavage.