1998 Volume 33 Issue 3 Pages 441-447
An insecticidal crystal protein (ICP) gene was cloned from Bacillus thuringiensis strain AF101 which has a low toxicity to the silkworm, Bombyx mori. The cloned AF101 ICP gene encoded 1, 182 amino acid residues and shared 93% homology with the cry1Ab gene of B. thuringiensis serovar kurstaki HD-1. In the amino-terminal portion of the activated toxin region of AF101 ICP, there were 18 amino acid differences when compared with HD-1 Cry1Ab, but only three amino acid differences in the hypervariable region of the activated toxin. The AF101 ICP gene was also found to contain the Cys-rich region observed in cry1Aa and cry1Ac in its carboxyl-terminal portion of the non-toxin region. In a bioassay of the cloned gene product, toxicity with intact AF101 ICP was nearly 17% less than that of HD-1 Cry1Ab. On the other hand, the activated toxin prepared from ICP by removing the non-toxin region was 9% less than that of HD-1 Cry1Ab. These results suggested that the specific toxicity of AF101 ICP against the silkworm correlated not only with its activated toxin region, but also with the non-toxin region.
