Wujie Su1, Jianwei Qu1, Yuying Ren1, Wenbing Wang2, Fanchi Li1, Bing Li3,4. 1. School of Basic Medicine and Biological Sciences, Soochow University, Suzhou, 215123, Jiangsu, People's Republic of China. 2. Department of Preventive Medicine and Public Health Laboratory Science, School of Medicine, Jiangsu University, 301 Xuefu Road, Zhenjiang, 212013, Jiangsu, China. 3. School of Basic Medicine and Biological Sciences, Soochow University, Suzhou, 215123, Jiangsu, People's Republic of China. lib@suda.edu.cn. 4. Sericulture Institute of Soochow University, Suzhou, 215123, Jiangsu, People's Republic of China. lib@suda.edu.cn.
Abstract
BACKGROUND: Currently, to delete an essential gene from a baculovirus genome, a cell line stably expressing the gene to be knocked-out should be first generated, which is time-consuming. Alternatively, essential genes can be deleted in E. coli using the λ Red recombination system, which requires an electroporation system. Here, based on homologous recombination in insect cells, we develop an alternative efficient system that requires neither generation of a cell line nor an electroporation system. METHODS AND RESULTS: Using puc19-based inverse PCR, a transfer vector for deleting BmNPV orf92 (Bm92, an essential gene) was efficiently constructed. A copy of Bm92 was introduced into the polyhedrin locus of BmNPV bacmid. The transfer vector was then co-transfected into BmN cell with the modified bacmid to enable homologous recombination at the Bm92 locus. An agarose-free approach was developed for the purification of Bm92-disrupted bacmid viruses in insect cells. Subsequently, BmN cells were co-infected with purified Bm92-disrupted bacmid viruses and unmodified bacmid viruses to allow recombination at the Tn7 insertion site between the two viruses. Finally, bacmid DNA extracted from BmN cells was transformed into chemically-treated competent DH10B cells, and blue colonies containing Bm92-disrupted bacmid were selected using PCR. CONCLUSIONS: For its efficiency and convenience, the system has great potential to be used for the generation of baculovirus knockout mutants.
BACKGROUND: Currently, to delete an essential gene from a baculovirus genome, a cell line stably expressing the gene to be knocked-out should be first generated, which is time-consuming. Alternatively, essential genes can be deleted in E. coli using the λ Red recombination system, which requires an electroporation system. Here, based on homologous recombination in insect cells, we develop an alternative efficient system that requires neither generation of a cell line nor an electroporation system. METHODS AND RESULTS: Using puc19-based inverse PCR, a transfer vector for deleting BmNPV orf92 (Bm92, an essential gene) was efficiently constructed. A copy of Bm92 was introduced into the polyhedrin locus of BmNPV bacmid. The transfer vector was then co-transfected into BmN cell with the modified bacmid to enable homologous recombination at the Bm92 locus. An agarose-free approach was developed for the purification of Bm92-disrupted bacmid viruses in insect cells. Subsequently, BmN cells were co-infected with purified Bm92-disrupted bacmid viruses and unmodified bacmid viruses to allow recombination at the Tn7 insertion site between the two viruses. Finally, bacmid DNA extracted from BmN cells was transformed into chemically-treated competent DH10B cells, and blue colonies containing Bm92-disrupted bacmid were selected using PCR. CONCLUSIONS: For its efficiency and convenience, the system has great potential to be used for the generation of baculovirus knockout mutants.