Intracellular cleavage of sigma A protein of avian reovirus

Abstract

By Western blot analyzes of expression of avian reovirus proteins, one unknown fragment was detected by an anti-sigma A monoclonal antibody in virus-infected cells lysate. It was interesting to note that RNA interference against sigma A resulted in the suppression of the unknown fragment. Using various lengths of sigma A constructs conjugated with different tags, we present evidences to demonstrate that the fragment comes from the cleavage of sigma A and is the larger carboxyl-terminus, termed sigma AC. Cleavage of sigma A simultaneously produces a smaller amino-terminus, named sigma AN. sigma AC 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 sigma A is common to all ARVs. Similar localization of sigma AC in both cytosol and nucleus with sigma A suggested that further modification of sigma A may be important for its function. Our evidences suggest that besides the outer capsid protein mu B, sigma A may also have post-translational cleavage which has never been reported before even in related mammalian reovirus. (C) 2010 Elsevier B.V. All rights reserved.