Reovirus protein sigma 1 translated in vitro, as well as truncated derivatives of it that lack up to two-thirds of its C-terminal portion, exists as two major tetrameric molecular species that differ in electrophoretic mobility.

Reovirus protein sigma 1 is the cell attachment protein that modulates tissue tropism and the nature of the antiviral immune response. This protein is present in reovirus particles in the form of 12 tetramers that are associated with the projections or spikes. We have analyzed a series of deletion mutants of protein sigma 1 in order to localize its oligomerization domain and found that progressive deletion from the C-terminus fails to affect ability to oligomerize, even when the deletion extends into the N-terminal heptapeptide repeat region. It was also found that native tetrameric protein sigma 1 synthesized in vitro, as well as its truncated derivatives, exists in two forms that differ in electrophoretic mobility. Possible reasons for this are discussed.