Influenza also replicates in the nucleus, but the activity of DDX21 against influenza appears not to require nucleic acid binding [60]; instead, a protein–protein interaction between DDX21 and the influenza PB1 polymerase inhibits the assembly of the viral replicase complex until being disrupted later in infection by increasing levels of the influenza NS1 protein [60]. This evidence concerns the gene DDX21 and influenza.