Viral dsRNA-activated oligoadenylate synthetase 3 (OAS3) exhibits a strong preference for long dsRNA. A study that included the crystal structure of the N-terminal enzymatically inactive 2'-5' oligoadenylate synthetase domain of human OAS3 (hOAS3.DI) in complex with 19-bp dsRNA indicated that this domain I (DI) subunit has high affinity for the binding of long (>50 bp) dsRNA, which then is presented to the enzymatically active C-terminal domain III (DIII) of OAS3 that produces 5’-triphosphorylated 2'-5' olgoadenylates from ATP (Donovan J et al. 2015). OAS3 was reported to be the major antiviral human OAS isoform (Li Y et al. 2016).