<p><b>A</b>. The <i>Gaussia princeps</i> luciferase-based complementation assay was performed with the PB2-Gluc1 and Gluc2-SMU1 fusion proteins, in the absence or presence of over-expressed RED protein. The Normalized Luminescence Ratios (NLR) were determined as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1004164#ppat-1004164-g001" target="_blank">Figure 1A</a>. The dashed line indicates the NLR cut-off that reduces false positive background below 2.5%, as determined using a random reference set of human proteins. The data are expressed as the mean +/− SD of triplicates and are representative of two independent experiments. <b>B</b>. The Gluc2-RED and Gluc1-SMU1 fusion proteins were co-expressed in HEK-293T cells, together with the wild-type PB2 protein or PB2-Strep fusion protein (transfection). Alternatively, HEK-293T cells co-expressing Gluc2-RED and Gluc1-SMU1 were superinfected with the rWSN or rWSN-PB2-Strep viruses (infection). Cell lysates were subjected to purification using StrepTactin beads. Control samples (cells co-expressing Gluc2-RED+Gluc1 or Gluc2+Gluc1-SMU1) were processed in parallel. Luciferase activities and NLRs were determined on an aliquot of the lysates (upper graph) and on the StrepTactin eluates (lower graph) as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1004164#ppat-1004164-g001" target="_blank">Figure 1A</a>. The data are expressed as the mean +/− SD of triplicates and are representative of two independent experiments (infection) or a single experiment (transfection).</p
