OAS1 (Oligoadenylate synthetase 1) is induced by type 1 interferon signaling. It recognizes 18 bp (or longer) double stranded RNA segments from invading viruses in the cytosol and catalyzes the production of 2’-5’ linked oligoadenylate (2-5A) from ATP. The 2-5A then, at the expense of yet more ATP, exclusively activates endoribonclease L (RNase L) by