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 HBV pgRNA deletion clones. Plasmid pHBV1.3 contains a 1.3 overlength HBV genome (Genbank Accession Number U95551), starting at nt 1000. The HBV nucleotide positions are according to Galibert et al . Cp represents the HBV core promoter. pA is the polyadenylation site. The arrow indicates the pgRNA transcription initiation site (nt 1820). Three major HBV mRNA (3.5 kb, 2.4 kb, and 2.1 kb) are depicted underneath the 1.3 mer HBV DNA template. The solid dot indicates 5’ cap of mRNA; and the sawtooth line represents the polyA tail at the 3’ terminus of mRNA. The internal deletion clones (pg-IDs) are described in details in S8 Fig. The terminal redundancy (TR) deletion clones contain truncations of HBV sequences (nt 1820–1918) at either 5’ or 3’ terminus of pgRNA coding sequences (pg-Δ5TR and pg-Δ3TR, respectively.), or both (pg-Δ5/3TR). The transcription of terminal truncated pgRNA is governed by CMV-IE promoter in the pCDNA3.1/V5-His-TOPO vector. (B) Sensitivity of HBV RNA with TR deletion to ISG20-mediated RNA reduction. HepG2 cells were transfected with HBV TR deletion clone and control plasmid or F-ISG20 plasmid. Cells were harvested at day 4 post transfection and subjected to viral RNA analysis by Northern hybridization. (C) HBV TR insertion renders Luc gene to be sensitive to ISG20. The schematic illustration indicates the reporter construct EnII/Cp-Luc with HBV TR insertion at the flanking non-translational region of luciferase ORF. HepG2 cells were transfected with each indicated reporter plasmid and control vector or plasmid expressing ISG20. Cells were lysed at day 3 post transfection and luciferase activity was measured. The plotted relative luciferase activity (RLA) represents the mean ± SD (n = 3) of the percentage of absorbance obtained from wells transfected with ISG20 over control vector.