Phylogenetic relationships of polymerase acidic (PA) genes of representative influenza A viruses.

<p>Details are as in the legends to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031844#pone-0031844-g001" target="_blank">Figures 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031844#pone-0031844-g002" target="_blank">2</a>.</p>