Amino acid clusters in NP of both the 1918 and pH1N1 strain mediate MxA resistance.

<p>(<b>A</b>) H5N1 polymerase activity in HEK293T cells after co-tranfection of the indicated expression plasmids coding for the NP mutants (100 ng) and MxA (200 ng). The activity in the presence of MxA was normalized to the activity observed with the inactive mutant MxA-T103A <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1003279#ppat.1003279-Ponten1" target="_blank">[66]</a>. The activity observed in the presence of pH1N1 NP was set to 100%. Error bars indicate the standard error of the mean of three independent experiments. Student's <i>t</i>-test was performed to determine the <i>P</i> value. *<i>P</i><0.05, ***<i>P</i><0.001, NS, not significant. Western blot analysis was performed to determine the expression levels of MxA and the indicated NPs. (<b>B–C</b>) Amino acid positions of NP mediating Mx resistance. The program PyMOL was used to assign the indicated positions based on the structural model of A/HK/483/97(H5N1) NP (PDB code:2Q06). Positions of adaptive mutations required for Mx resistance of the 1918 NP are marked in blue (B). Amino acids of pH1N1 NP that exhibit only minor contribution to Mx resistance are highlighted in light red, whereas amino acids that strongly increased Mx resistance are indicated in red (C).