The M segment polyprotein.

<p>Schematic summary of the viral proteins expressed from the M segment. <b>Fig. 1.A.</b> Translation from the M segment RNA can start at five start codons with methionine in amino acid (<u>aa</u>) positions 1, 39, 52, 131 and 136. All proteins are expressed using the same reading frame. The polyprotein has N-glycosylation sites at <u>aa</u> positions 88, 438, 794, 829, 1035 and 1077, and two cleavage sites between positions 153 and 154, and 690 and 691. The signal peptide (1–16 <u>aa</u>) is represented by a black thicker short line at the very N-terminus. <b>Fig. 1.B.</b> Different proteins are generated depending on the start codon used for the protein synthesis. Translation starting with methionine in position “1” yields LGp and Gc glycoproteins due to a cleavage at position 690/691. Both glycoproteins are fully glycosylated. Translation starting with methionine in <u>aa</u> position 39 yields three proteins: nonstructural NSm protein where the N-glycosylation site at <u>aa</u> position 88 may not be utilized, and two glycoproteins Gn and Gc due to cleavage in positions 153/154 and 690/691. No product has been identified for the putative starting methionine in position 52. Translation starting with methionine either at 131 or 136 position yields glycoproteins Gc and Gn, using the 690/691 cleavage site. Gn and Gc glycoproteins are considered to be fully glycosylated. Based on <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087385#pone.0087385-Collett1" target="_blank">[2]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087385#pone.0087385-TorborgKakach1" target="_blank">[3]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087385#pone.0087385-Gerrard1" target="_blank">[4]</a>.