The invention describes novel pharmaceutical compositions for the treatment of virus infections and cancer. The pharmaceutical compositions include mutant oligoadenylate synthetases (OAS) that have either enhanced cell permeability, reduced oxidative potential, improved antiviral activity, improved enzymatic activity, or absent enzymatic activity. The pharmaceutical compositions have improved drug properties and retain or have enhanced antiviral activity relative to their native forms. The pharmaceutical compositions further include chemically modified oligoadenylate synthetases, such chemical modifications being designed to increase serum stability and reduce immunogenicity in vivo. Such chemical modifications further increase drug stability and manufacturability in vitro. Compositions composed of more than ninety novel modifications are described. Also described are antibodies to polypeptides of the invention.