Location of a lepidopteran specificity region in insecticidal crystal protein CryIIA from Bacillus thuringiensis

The Bacillus thuringiensis insecticidal crystal protein CryIIA has both high mosquito activity and gypsy moth activity; in contrast CryIIB, which is 87% homologous, displays no mosquito activity and has a three-fold lower gypsy moth activity. The regions responsible for specificity against gypsy moth (Lymantria dispar) and mosquito (Aedes aegypti) larvae were located by introducing MluI and XhoI sites into homologous positions within the putative domain II of both cryIIA and cryIIB genes, which divided almost equally the respective second domains into three regions. Taking advantage of naturally occurring NheI and NarI sites that border the putative domain II, a set of seven chimeric proteins were produced by exchanging all combinations of those regions between CryIIA and CryIIB. Analysis of the toxicity of these chimeric proteins demonstrated that the lepidopteran and dipteran specificity regions of CryIIA were not colinear. While the specificity region of CryIIA against mosquito larvae involved region 1 and probably also region 2, the specificity region of CryIIA against gypsy moth larvae was located within region 2.