Many Cry1 mutant toxins were developed which resulted in
low or no toxicity on tested insects by protein engineering
techniques such as (a) single or multiple amino acid changes
in variable and conserved regions through site directed
mutagenesis
(b) restriction fragment exchange between
closely relatedcrytoxin genes or with other bacterial toxin
genes and
(c) exchange of domains between toxin genes
through PCR mediated cloning or in vivo recombination in
recAþ(recombinant proficient) Eschericha coliStrains.
This
has helped to define better the functions of these crystal
protein helices in membrane binding, membrane insertion
and toxicity. Various mutations in domain I, II and III of the
crystal toxins and their effect on the toxicities toward the
target insects and trypsin stabilities have been presented in
Table 2.