Interferon-inducible ribonuclease ISG20 inhibits hepatitis B virus replication through directly binding to the epsilon stem-loop structure of viral RNA
(A) Schematic illustration of ISG20. The amino acid (a.a) positions are labeled with numbers. The gray boxes indicate the predicted Exo motifs. The enzymatic mutant site (D94G) is marked with an asterisk. (B) Bacterially expressed His-tagged ISG20 and mutants were purified and examined by SDS-PAGE Coomassie staining. The asterisk indicates a nonspecific protein band co-purified with the recombinant ΔExoII mutant. (C) EMSA of ε binding by wildtype ISG20 and the indicated mutants. (D) HepG2 cells were co-transfected with pHBV1.3 and control vector or indicated FLAG-ISG20 constructs. HBV RNA and ISG20 proteins were detected by Northern and Western blot, respectively.