Stimulates translation by blocking the activation of the dsRNA-dependent protein kinase EIF2AK2/PKR, thereby inhibiting the host interferon response. Sigma3 prevents the activation of EIF2AK2 by competing with the kinase for dsRNA-binding. The viral outer shell polypeptides, of which sigma-3 is one, impose structural constraints that prevent elongation of nascent transcripts by the RNA-dependent RNA polymerase lambda-3. Heterohexamer of three sigma-3 and three Mu-1 proteins (By similarity). The RNA-binding form is probably a homodimer. Found in the outer capsid. Each subunit is positioned with the small lobe anchoring it to the protein mu1 on the surface of the virion, and the large lobe, the site of initial cleavages during entry-related proteolytic disassembly, protruding outwards. Cleaved during virus the endosomal proteolytic disassembly of the outer capsid. Belongs to the orthoreovirus sigma-3 protein family.