Schematic representations of SARS-CoV M mutations.

<p>Wild-type (wt) SARS-CoV M protein is shown with three predicted transmembrane domains (shaded boxes). Amino acid substitutions at M codon positions are indicated. An HA or FLAG epitope tagged at the amino or carboxyl terminus is designated as HA-M and M-FLAG, respectively. W57A/L and F95A/L indicate an Ala or Leu substitution at W57 and F95. Alanine substitutions of the di-leucine motif at codons 15–16 and 218–219 are designated as 15LL/AA and 218LL/AA, respectively. Underlined mutations denote that changing the aromatic residue to Ala or Leu markedly affected M secretion, but replacement with another aromatic residue did not. The ability for each construct to release or produce VLPs with coexpressed N is summarized in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0064013#pone-0064013-t001" target="_blank">Table 1</a>.