Insect-resistant tomato line 5345 was developed using recombinant
DNA techniques to express the insecticidal protein, Cry1Ac, encoded
by the cry1Ac gene from the soil bacterium Bacillus thuringiensis
subsp. kurstaki strain HD73.
Insecticidal activity is caused by the selective binding of Cry1Ac
protein to specific sites localized on the brush border midgut
epithelium of susceptible lepidopteran species. Following binding,
cation-specific pores are formed that disrupt midgut ion flow
thereby causing gut paralysis and eventual death from bacterial
Delta-endotoxins, such as the Cry1Ac protein expressed in tomato
line 5345, exhibit highly selective insecticidal activity against a
narrow range of lepidopteran pests. The specificity of action is
directly attributable to the presence of specific receptors in the
target insects. There are no receptors for delta-endotoxins of B.
thuringiensis on the surface of mammalian intestinal cells,
therefore, livestock animals and humans are not susceptible to