Intracellular cleavage of σA protein of avian reovirus

By Western blot analyzes of expression of avian reovirus proteins, one unknown fragment was detected by an anti-σA monoclonal antibody in virus-infected cells lysate. It was interesting to note that RNA interference against σA resulted in the suppression of the unknown fragment. Using various lengths of σA constructs conjugated with different tags, we present evidences to demonstrate that the fragment comes from the cleavage of σA and is the larger carboxyl-terminus, termed σAC. Cleavage of σA simultaneously produces a smaller amino-terminus, named σAN. σAC could be seen early in viral infection and accumulated with time and dose of infection, indicating that the derived products are not just transient intermediates of protein degradation. The same type of cleaved products were also observed in different genotypes and serotypes of ARV as well as in different cell lines, suggesting that this intracellular modification of σA is common to all ARVs. Similar localization of σAC in both cytosol and nucleus with σA suggested that further modification of σA may be important for its function. Our evidences suggest that besides the outer capsid protein μB, σA may also have post-translational cleavage which has never been reported before even in related mammalian reovirus.