Differential effects of helper proteins encoded by the cry2A and cry11A operons on the formation of Cry2A inclusions in Bacillus thuringiensis.

To compare the differential effects of cry2A operon orf2 (29-kDa protein gene) and Cry11A operon orf3 (20-kDa protein gene) on Cry2A synthesis and inclusion formation, we expressed the cry2A gene along with either the 29-kDa gene, 20-kDa gene, or both genes. Constructs containing 20-kDa, in the presence or absence of 29-kDa, produced more Cry2A than constructs which lacked this gene. Cry2A synthesis was also higher when the 29-kDa gene was included with 20-kDa in the construct. However, even in the presence of increased Cry2A synthesis facilitated by the 20-kDa gene, typical Cry2A crystals did not form if the 29-kDa gene was not included in the construct. These results suggest that the 29-kDa and 20-kDa proteins have different functions, with the 20-kDa protein acting like a molecular chaperone to enhance net Cry2A synthesis, and the 29-kDa protein likely serving as a template for the stabilization of Cry2A molecules and their organization into the rectangular inclusion characteristic of wild-type Cry2A crystals.