GENETIC-ANALYSIS OF THE CRY1AB GENE IN BACILLUS-THURINGIENSIS STRAIN AF101

An insecticidal crystal protein (ICP) gene was cloned from Bacillus th uringiensis strain AF101 which has a low toxicity to the silkworm, Bom byx mori. The cloned AF101 ICP gene encoded 1,182 amino acid residues and shared 93% homology with the cry1Ab gene of B. thuringiensis serov ar kurstaki I-ID-I. In the amino-terminal portion of the activated tox in region of AF101 ICP, there were 18 amino acid differences when comp ared with HD-1 Cry1Ab, but only three amino acid differences in the hy pervariable 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 to xin prepared from ICP by removing the non-toxin region was 9% less tha n that of I-ID-I Cry1Ab. These results suggested that the specific tox icity of AF101 ICP against the silkworm correlated not only with its a ctivated toxin region, but also with the non-toxin region.