Abstract:
Expression of chitinase gene of Thai isolated Helicove~n armigera single nucleocapsid nucIeopolyhedrovirus (Th-HaSNPV) in baculovirus expression insect cell system was performed in this study using Atttographa califomica multinucleocapsid nuleopolyhedrovirus (AcMNPV) bacmid, baculovirus-bacteria shuttle vector. HaSNPV chitinase gene was inserted into AcMNPV bacmid by transposition at transposon attachment site in E. coIi (DHIOB~cCe lls). Recombinant AcMNPV bacmid with HaSNPV chitinase gene inserted into its genome via transposition process was purified &om bacteria and confumed by PCR analysis- The recombinant bacmid was used for transfection into insect cells. During transfeetion, recombinant baculovirus particles were formed and released to infect into neighboring insect cells to produce recombinant HaSNPV chitinase
enzyme. SDS-PAGE and active-PAGE analysis were performed to detect expression of recombinant HaSNPV chitinase. However, the HaSNPV chitinase expression can not be confumed since the expression of AcMNPV chitinase gene of bacmid itself was also observed at approximately the same molecular weight. In order to use the AcMNPV bacmid as an expression vector fix HaSNPV chitinase gene, AcMNPV chitinase gene expression in AcMNPV bacmid must first be interrupted. In Phis study, insertion of GFP gene in the middle of AcMNPV chitinase gene by homologous recombination was performed for AcMNPV chitinase gene disruption. Two homologous sequences for recombination were tested. The fmt sequence was the use of HaSNPV chitinase which had 66% identity to the AcMNPV bacmid on the pNVBGFP as homologous region. Recombinant AcMNPV
bacmid infected into insect ceU (SF-9) produced virus progeny with green fluorescent. Isolation of recombinant AcMNPV bacdovirus expressing GFP was performed by 4 rounds plaque purification which takes long time (4-6 weeks). An alternative method for selection of recombinant bacmid was therefore proposed Since the AcMNPV bacrnid is bacdovirus-bacteria shuttle vector, colony
selection method was choosen. A single colony was selected. Confiation of GFP gene insertion into A c Wba cmid extracted from each colony was performed by PCR analysis and recombinant bacmid expressing GFP can be selected in shorter time (1-2 weeks). However, analysis of insertion of GFP gene into AcMNPV chitinase gene by PCR shows no GFP gene at specific chitinase gene. The second sequence with 1Wh homology (AcMNPV chitinasel was therefore used. It was found that after homologous recombination, the recombinant baculovhs expressing GFP had GFP gene inserted at specific AcMNPV chitinase gene and no acitivity of AcMNPV chitinase in infected insect cells which infected by this recombinant AcMNPV baculovirus was observed. This study demonstrated that homologous recombination method (with high % homology of homologous sequence) can be applied with AcMNPV bacmid for genetic engineering of any genes of the bacmid rather than limiting at the transposition attachment site that is generally used of barmid. In addition, colony selection of recombinant bacmid after homologous recumbination can be used for separation of recombinant and parental bacmid in shorter time compare to plaque purification.