Intracellular proteolysis and limited diversity of the Bacillus thuringiensis CryIA family of the insecticidal crystal proteins.

The current concept of how the highly homologous Bacillus thuringiensis insecticidal crystal protein genes (cry genes) evolved is through recombination among themselves. The cryIA gene family, which is more than 80% identical, consists of only three known genes, even through they are often found together in the same bacterium. To examine the lack of diversity among these genes, recombinatorial chimeric protein toxin genes were constructed and transformed into E. coli, B. subtilis, and B. thuringiensis. Of the nine chimeric proteins examined in this work; three were degraded in E. coli, five in B. subtilis, and seven in B. thuringiensis, suggesting that most Cry proteins resulting from recombination events are degraded by intracellular proteases that are particularly prevalent in B. thuringiensis.