Double-stranded RNA-dependent protein kinase (PKR) is regulated by reovirus structural proteins

Abstract

Reovirus σ3 is a virion outer shell protein that also binds dsRNA and stimulates translation by blocking activation of the dsRNA-dependent protein kinase, PKR. Purified σ3 was shown by gel shift assay to bind specifically to RNA duplexes of minimal length 32-45 base pairs. PKR binding to dsRNA was prevented by σ3, and translation inhibition of luciferase reporter by PKR expression in transfected cells was reversed by σ3. Association of σ3 with its outer capsid partner μ1/μ1 C eliminated dsRNA binding and prevented restoration of protein synthesis. Analyses of σ3 mutants demonstrated a direct correlation between dsRNA binding and reversal of the down-regulation of translation by PKR. In infected cells, σ3 was stable but dsRNA binding decreased, presumably due to μ1/μ1C complex formation. The results suggest a functional transition from early inhibition of PKR activation by σ3 to its association with μ1/μ1C in capsid structures.