OAS3 binds to dsRNA with higher affinity than do OAS1 or OAS2 in intact cells. (A) A549 cells were transfected with empty vector (mock) or plasmids encoding Flag-tagged OAS1 p42, OAS1 p46, OAS2, or OAS3 and then were transfected with pIC-biotin. Streptavidin bead pull downs or proteins were carried out and were analyzed by immunoblotting with anti-Flag antibody. The blot was exposed for 5 or 20 min. Immunoblots without pull down show input levels of OAS proteins and GAPDH loading and transfer control. The additional, faster-migrating band in the p46 lanes is most likely a breakdown product of p46. (B) A549 cells were treated with IFN-β (1,000 U/mL) and then were transfected with pIC-biotin. Streptavidin bead pull down of pIC-biotin bound proteins was carried out and probed by immunoblotting with antibodies against OAS1, OAS2, and OAS3. Input levels of proteins are also shown. Thirty-fold more protein was used for pull down compared with input protein on the immunoblot.