Mutant del20NLS-NP is expressed and localized in the nucleus and cytoplasm as WT-NP. 293 T cells were transfected with plasmid mixes to express reconstituted vRNPs containing influenza RdRP with vRNA templates and either WT-NP, del20NLS-NP, or vector control as indicated. Cells were fractionated and protein extracts from both the cytoplasm and nucleus were analyzed by western blot. Anti-FLAG antibody detects the C-terminal epitope tag of both WT-NP and del20NLS-NP. Hsp90 is a protein localized to the cytoplasm while Nxf1 is localized to the nucleus, demonstrating cellular fractionation with only slight cross contamination of cellular fractions. Shown is a representative experiment, repeated more than three times.