Two polar residues within C-terminal domain of M1 are critical for the formation of influenza A Virions

The matrix protein 1 (M1) is the most abundant structural protein in influenza A virus particles. It oligomerizes to form the matrix layer under the lipid membrane, sustaining stabilization of the morphology of the virion. The present study indicates that M1 forms oligomers based on a fourfold symmetrical oligomerization pattern. Further analysis revealed that the oligomerization pattern of M1 was controlled by a highly conserved region within the C-terminal domain. Two polar residues of this region, serine-183 (S183) and threonine-185 (T185), were identified to be critical for the oligomerization pattern of M1. M1 point mutants suggest that single S183A or T185A substitution could result in the production of morphologically filamentous particles, while double substitutions, M1-S183A/T185A, totally disrupted the fourfold symmetry and resulted in the failure of virus production. These data indicate that the polar groups in these residues are essential to control the oligomerization pattern of M1. Thus, the present study will aid in determining the mechanisms of influenza A virus matrix layer formation during virus morphogenesis.