CLONING AND EXPRESSION OF THE CRY1EA4 GENE OF BACILLUS-THURINGIENSIS AND THE COMPARATIVE TOXICITY OF ITS GENE-PRODUCT

A new cry gene (cry1Ea4) was cloned and sequenced from a Bacillus thur ingiensis isolate native to Mexico (LBIT-147). The gene coded for a 13 3 kDa protoxin which had greater than 99% homology with the holotype C ry1Ea1, as only four mismatches were found between the two amino acid sequences. When the Cry1Ea4 toxin was expressed in a crystal-negative strain of B. thuringiensis, bipyramidal crystals were produced. Purifi ed crystals from this recombinant strain and from the holotype (Cry1Ea 1) were bioassayed against first instar larvae of the tobacco hornworm . Statistically different mean LC50 values indicated that Cry1Ea4: was more toxic than its holotype. This increase in toxicity may be attrib uted to the three amino acids which differ from the holotype sequence in the toxic fragment.