Recently, Bacillus thuringiensis (Bt) cry genes encoding insecticidal Cry proteins have been widely applied for the construction of transgenic crops resistant to insect pests. This study aimed to construct novel mutant cry1Ac genes for genetically modified crops with enhanced insecticidal activities. Using multi-site directed mutagenesis, 34 mutant cry1Ac genes were synthesized and converted at 24 amino acid residues, located on domain I (8 residues) and domain II (16 residues). These mutant genes were expressed as a fusion protein with polyhedrin using the baculovirus expression system. The expressed proteins were occluded into polyhedra and activated stably to 65 kDa by trypsin. Among these, Mut-N04, N06, and N16 showed high levels of insecticidal activites against larvae of Plutella xylostella, Spodoptera exigua, and Ostrinia furnacalis. Mut-N16, which showed the highest insecticidal activity, is expected to be a desirable cry gene for introduction into transgenic crops. This study could provide useful means to construct mutant cry genes with improved insecticidal activities and expanded host spectrum for transgenic crops.

• Jong Hoon Kim(Department of Agricultural Biotechnology, Seoul National University)
• Song Eun Kim(Department of Agricultural Biotechnology, Seoul National University)
• Jae Young Choi(Research Institute for Agriculture and Life Sciences, Seoul National University)
• Seok-Hee Lee(Department of Agricultural Biotechnology, Seoul National University)
• Ying Fang(Department of Agricultural Biotechnology, Seoul National University)
• Kyu Baik Ha(Department of Agricultural Biotechnology, Seoul National University)
• Dong Hwan Park(Department of Agricultural Biotechnology, Seoul National University)
• Woo Jin Kim(Department of Agricultural Biotechnology, Seoul National University)
• Yeon Ho Je(Department of Agricultural Biotechnology, Seoul National University)