Supported by National Health Research Institutes (NHRI-EX94-

AIM: To study the baculovirus/mammalian cell system for effi cient expression of functional large hepatitis delta antigen (L-HDAg). METHODS: A recombinant baculovirus expressing histidine-tagged L-HDAg (L-HDAgH) was constructed to transduce baby hamster kidney (BHK) cells by a simplifi ed transduction protocol. RESULTS: The recombinant baculovirus transduced BHK cells with efficiencies higher than 90 % as determined by fl ow cytometry. The expression level was signifi cantly higher than that obtained by plasmid transfection and was further enhanced 3-fold to around 19 pg/cell by the addition of 10 mmol/L sodium butyrate. Importantly, the expressed L-HDAgH was localized to the cell nucleus and correctly isoprenylated as determined by immunofluorescence labeling and confocal microscopy. Moreover, L-HDAgH interacted with hepatitis B surface antigen to form virus-like particles. CONCLUSION: The fusion with histidine tags as well as overexpression of L-HDAgH in the baculovirus-transduced BHK cells does not impair the biological functions. Taken together, the baculovirus/mammalian cell system offers an attractive alternative for high level expression of L-HDAgH or other proteins that require extensive post-translational modifi cations. © 2006 The WJG Press. All rights reserved