EXPRESSION OF CRYIVA AND CRYIVB GENES, INDEPENDENTLY OR IN COMBINATION, IN A CRYSTAL-NEGATIVE STRAIN OF BACILLUS-THURINGIENSIS SUBSP ISRAELENSIS

The cryIVA and cryIVB genes, encoding the 125- and 135-kDa proteins, r espectively, of Bacillus thuringiensis subsp. israelensis, were cloned either alone or together into a shuttle vector and expressed in a non toxic strain of B. thuringiensis subsp. israelensis. The CryIVB protei n was produced at a high level during sporulation and accumulated as i nclusions; in contrast, the CryIVA polypeptide did not form such struc tures unless it was cloned on a higher-copy-number plasmid. Transcript ional fusions between the cryIVA or cryIVB gene promoter and the lacZ gene were constructed. The poor synthesis of CryIVA was not due to a p oor efficiency of transcription from the cryIVA gene promoter. Mosquit ocidal assays performed with purified inclusions showed that CryrVA wa s toxic for larvae of the species Aedes aegypti, Anopheles stephensi, and Culerpipiens, whereas CryIVB displayed activity only toward Aedes aegypti and Anopheles stephensi. The activity of inclusions containing both polypeptides was higher than that of single-peptide inclusions b ut was not as high as that of the native crystals, which contain at le ast four polypeptides.