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Appl Environ Microbiol. 1996 January; 62(1): 279–282.
PMCID: PMC167797

Site-directed mutations in the third domain of Bacillus thuringiensis delta-endotoxin CryIAa affect its ability to increase the permeability of Bombyx mori midgut brush border membrane vesicles.


A series of mutant Bacillus thuringiensis CryIAa delta-endotoxin proteins was prepared by replacing the first, second, and last arginine residues of the conserved third-domain sequence, R-521 YRVRIR-527, with other amino acids. The stable mutant proteins were bioassayed against Bombyx mori larvae and found to all be approximately half as active as wild-type CryIAa. The toxins were also tested by means of a light-scattering assay for their ability to increase permeability of larval B. mori midgut brush border membrane vesicles. Three of the mutant toxins were as active as the wild-type toxin in the vesicle permeability assay.

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