To investigate whether the dynamics of PIAS1 expression is affected during IAV infection, we infected A549 cells with WSN (H1N1) virus at an MOI of 0.1 and determined the expression of PIAS1 by western blotting at 0, 12, and 24 h p.i. We found that the level of PIAS1 expression gradually increased as the infection progressed (S5A Fig). Here, PIAS1 is linked to infection.