Localization of isoprenylated antigen of hepatitis delta virus by anti-farnesyl antibodies

Hepatitis delta virus (HDV) is a subviral pathogen that requires pre-existi ng or concurrent infection with hepatitis B virus (HBV), HDV expresses two forms of a single protein, the delta antigen (HDAg), which are identical ex cept for an additional 19 residues at the C terminus of the large form, Wit hin this C-terminal extension a cysteine residue is isoprenylated; this iso prenylation is critical for interaction with HBV envelope proteins to enabl e virus assembly and release into the medium, Therefore, large HDAg must be recruited to an extracellular compartment. However, immunostaining with HD Ag-specific antibodies has localized the large antigen mainly to the nucleu s and supports the notion that large HDAg suppresses virus replication in t he nucleus, Since isoprenylation would increase the hydrophobicity of the p rotein and may favour transport towards specific membranes, the question re mains whether the large HDAg detected in the nucleus carries an isoprenyl g roup. To address this issue, antibodies against the farnesyl modification w ere generated to allow direct visualization of the antigen by immunofluores cence microscopy, The antifarnesyl antibodies specifically stained large HD Ag expressed in Huh-7 cells, and the signal was largely restricted to the n ucleus; the staining pattern could be superimposed on those of cells staine d for large HDAg, The large HDAg translocated into the nucleus was therefor e isoprenylated, in addition, antibodies specific for the farnesyl modifica tion should be applicable to the study of other similarly isoprenylated pro teins.