Upon transient expression in HEK-293T cells and subsequent infection with the WSN virus, the Strep-tagged proteins were purified (Fig. 5d) and the PB2, NP, NA, NS1 and NS2 mRNAs were quantified by RT-qPCR on 1 μg of RNA extracted from the cell lysate (C) and eluate (E) fractions. This evidence concerns the gene XK and infection.