The cry1Ac gene produces the insect control protein Cry1Ac, a
delta-endotoxin. The Cry1Ac protein produced in MON531 is almost
identical to that found in nature and in commercial Bt spray
Cry proteins, of which Cry1Ac is only one, act by selectively
binding to specific sites localized on the lining of the midgut of
susceptible insect species. Following binding, pores are formed
that disrupt midgut ion flow, causing gut paralysis and eventual
death due to bacterial sepsis.
Cry1Ac is insecticidal only when eaten by the larvae of
lepidopteran insects (moths and butterflies), and its specificity
of action is directly attributable to the presence of specific
binding sites in the target insects. There are no binding sites for
delta-endotoxins of B. thuringiensis on the surface of mammalian
intestinal cells, therefore, livestock animals and humans are not
susceptible to these proteins.