2'-5'-oligoadenylate synthetase 3 (OAS3) is a template-independent nucleotidyl transferase that, once activated by double-stranded RNA in the cytosol, produces second messenger molecules 5'-triphosphorylated 2′,5′-linked oligoadenylates (2-5A). OAS3 was reported to produce preferentially dimeric 2-5A (Rebouillat D et al. 1999). However recent reports showed that OAS3 is able to synthesize 2',5'-oligoadenylates of sufficient length (the triadenylate and longer) to activate RNase L and thus limit viral propagation (Ibsen MS et al. 2014; Li Y et al. 2016).